Sunday, December 19, 2010

On the design of very high RPM camshaft profiles minimizing valve float dangers

Discussion to this video:

and another in which three springs stabilise and holde valve stem so that it does not float at all.

There are many vastly improved camshafts on the market which give you more power, but sometimes you want to reach higher RPM and need to know how. Harder springs is certainly the answer, but one answer you might not heard is camshaft profile which properly handles the returning valve propeled by spring.
Valve float is created when the camshaft recedes so fast that it outruns the valve. You can correct it by using stronger springs or using less steep cam profile. Well the less steep profile is hardly practical, is it? Generally yes, it could make the cam overlap into useless area. So you use harder springs to reach higher RPM instead. But again, you can not do it endlessly. What to do next? Consider the cam profile again. While valve float is hazard, the true bad thing is valve bounce where the valve 'slams close' and then shortly opens. We want it 'close shut', not 'slam'. How about... if we closed on a steep profile first (the valve is propelled by the spring and flies freely), but then in the final part where the valve would have little useable lift in airflow terms we designed the profile as such to catch the valve and decelerate it slowly.

The equation on the linear movement of the valve should be such that the da/dt rises linearly from zero to a certain value and decreases in the same manner. (where acceleration a = dv/dt and speed v = ds/dt). The d(da/dt) /dt value can be zero. In other words: the acceleration should have acceleration too, not just jump to a certain value.
You then must convert the designed valve movement into cam profile, depending on your actual mechanism dimensions, then grind new cam profile.

Ideally, the valve and springs should be at all times touching the rocker arm, pressing hard against it, but in racing we sometimes trade longevity for victory. However, properly designed downslope of a cam does have a mechanical advantage over straight acceleration jump even when no valve float occurs!

Next thing you want to hear the engine head has is: 'hydraulic lifters' (not hydraulic actuators, hydraulic valve pads) . Why? Think of them as dampeners able to absorb the returning shock of the flying bullet - which valve stem propeled by a spring certainly is, so that the valve does not bounce back, but releases the energy into the hydraulic fluid and sits down. This of course requires certain construction of the hydraulic valve lifters, but first thing is you have to have them first.

By the way, if you are aware of CFD software, which is free and simulates the supersonic thermoacoustic effects correctly, let me know. Because in 2-cycle engine this is what you want and need and nothing less is quite satisfactory.

Thursday, November 20, 2008

The great comparision table of injector piston-barrel elements for Bosch MW pumps for our beloved Mercedes cars.

Hello all fellow visitors, colleagues and especially, my dear, beloved lab rats.

The long promised table of many MW injector pump elements is at http://spreadsheets.google.com/pub?key=pZMMSqp3uSZdyqyAJ0XqRCA

I hope you appreciate the long, hard work :)

Now some notes for those visiting this page directly, it is about replacing 5.5mm diameter piston-barrel MW injector elements with 8mm, 9mm, 10mm (preferably) or even 11mm types.

As far as the superturbo modification go, please, take care so that the maximum combustion pressure will not blow the head gasket away, nor terminally damage rod bearings.
To do that, you may really want to limit the maximum fuel delivery and keep all the limiters in governor inside, you really may appreciate that they are there to save your engine!
Also, you will want to experiment with injection timing and bring the beginning of injection closer to TDC. One of the reasons is that the injection of the same amount of fuel may be finished 2x to 4x sooner than originally designed, so the fuel will have more time to combust and therefore reaching peak pressure sooner and we want this happen at or after the top dead center. (YRMV)

This, under extreme settings, may bring more white smoke, but under lead foot the maximum pressure peak may be dissolved in rapidly proceeding expansion due to piston downward movement. This will rob you of some horsepower, but it also greatly reduces stresses on your piston, head, gasket, bearings. I suggest this move for maximum power modifications, or any other application where emissions are irrelevant, but absolute maximum achieveable power is important. You can see something like that in tractor pulling, where start of injection begins at 50°before TDC and ends in a similar fashion. But hey, 2MW is not what we want here, right?

Injecting much fuel after, say 30°TDC will increase power output without increasing stress, but the efficiency of doing so is lower than with injecting fuel well in advance.

Also, overall injection time will be one third of original for the same engine power output and this gives you great chances on reducing engine emissions.
My advice is then: keep the maximum pressure down and heat will also be less of a problem, even if the temperatures will be high, it is the pressure what deforms objects, heat only makes them weaker.

My last advice: different, more durable bearing material for the crankshaft and piston rods. If you are going to increase the stresses, you have to prepare the bearings accordingly.

P.S. I am great fan of synthetic 10W-60 oil too, used in short exchange intervals.

As you will notice, I added a Donate button, yes I dropped down that much, I simply have to admit that spending countless hours doing research means doing less (or no) work I might be paid for.

If anyone here after reading that long page will need any aid in purchasing a specific element set, I will go to ask distributor(s) if or when they will be able to provide web interface for you.

Thank you for your input.

Sunday, October 19, 2008

Rotating Non-Equilibrium Gliding Arc Plasma Disc for Enhancement in Ignition and Combustion of Hydrocarbon Fuels

No, I am not author of the above title, I just realized the importance of the document for diesel cars!

still searching for the link where it came from!

I have good news for you. The above mentioned document can be used as a cetane number improver for diesel engines, by making a lot of radicals in the suction air! I have yet to try it, but in theory it is worth a try! If nothing else, it takes much less power than a H2 generator and has much higher efficiency!

I will repeat the abstract here:
The best plasma discharge system for combustion applications should generate non-equilibrium plasma with high concentration of active species and intermediate temperatures, high enough to support chain in propagation reaction. The non-equilibrium Gliding Arc (GA) aptly suits this application. A novel, nonequilibrium gliding arc plasma disc reactor has been developed to study possibility of flame speed increase, flammability limit extension for hydrocarbon fuel and oxidizer mixture.
What does it mean? To simplify that paper: you remember why nailing occurs? It is because fuel is dispersed in prechamber but fails to combust. The same happens if you increase the injection pressure past 140BAR, the fuel is sprayed nice and lovely, but the droplet is too small and too fast to keep a burning flame behind it and the flamelet goes out, only to result in detonation of the vapour later. (that is the flammability limit mentioned above!) Air full of nitrogen oxides and intermediate products is very reactive and the paper shows some good increase of resistance of diffuse flame to go out with increasing wind speed.

So intended use?
You install it in suction, even before the air filter. Power it up, run the engine. Now Injection pressure can be adjusted to the point where the injector will have a tendency to make knocking sound. If 20% better combustion speed is achieved, the injection pressure where this happens may be higher some 6-9%, I reasonably expect it to raise from 135-140BAR to 145-150BAR. Not that it is a big improvement, but every improvement of the combustion profile is improvement of engine efficiency!

Next, if this is proved, or maybe not, we can adjust IP timing, perharps retarding it one or two degrees. (moving closer to the top dead center).

One note: oil life might be negatively affected if you put it into much contact with the reactive air. Not by much, only few percent - because it is already in contact with combustion gases, but I thought you might want to know.

Friday, July 18, 2008

Hard anodizing in warm baths!

So, I developped hard anodizing process that does not require supercooled sulphuric acid. One of the keys are bath additives. The other is current density (with large surface parts, cooling may be needed, the third and most important is to make the process start at the surface. And that one seems to be the hard part.

It is easy to form a hard anodized layer ( a dark brownish-gray thick layer ) once it started forming and this may be the property that one german company uses to form 15 micron hard anodized layer in just one minute and do it selectively! Gramm Technik link here.

Theory behind hard anodizing (type III anodise) - You need higher current density and you need high voltage. Sulphuric acid has high conductivity at high temperatures which will limit your ability to reach any higher voltage in the bath. Also high current baths get warm very quick. So cooling has to be used, ideally to the point that the bath is ready to freeze. That makes 1) the acid attack the formed oxide less and 2) the intrictic conductivity of the bath is lower, it is easiet to reach high voltage.

I simplified the above a bit, but here is what I have done: I decreased the bath conductivity without diluting the 8% sulphuric acid at room temperatures. The ability of the bath to attack the oxide is also lower. Bad points: some reaction may allow appearance of self-catalyzed burning holes on the anode, these may eat the aluminium out without stopping. This can be cured by simply tuning off the current for a second, or by rising the part above the bath surface. Then anodizinfg resumes normally.

What I found out is that the surface of the aluminium is very quickly covered by whitish protective oxide layer after turning the current on. Initial current is high, but quickly falls off and the layer does not seem to grow substantially if at all. That is at 30V voltage! No oxygen bubbles on the anode.

I have to note hat I use only mechanically cleaned and freshly polished alu samples, no chemical cleaning, or HF acid cleaning (or nitric acid). After some time the first oxide will be eaten trough and hard anodised layer will start to form. This happens mostly at the bath-air interface and follows straight down - propapbly some kind of salt created there activates the surface. After that the hard layer spreads to the sides and some aluminium thickness is removed in the process. Anyway, the created layer is not scratchable by a nickel coated metal probe of the multimeter.

Next point of achievement was bringing the cathode closer to the anodized sample and the current went up fivefold to tenfold. I did that on anothers alu sample and the overall thickness went up from 0.3mm to 0.35mm! That means the oxide layer is far thicker than 50 microns! Again, little or NONE oxygen bubbles on the anode.

Tuesday, July 01, 2008

Air boosting driven by exhaust powered vacuum.

The basic idea goes like this: to make 20% boost on an OM617 engine at full RPM you need about 2.5kW of power in case of adiabatic compression. I used adiabatic process calculator and here are the numbers. 135 L of air compressed to 112.5 Litres from starting pressure of 98.94 kPa and end pressure of 127.71 kPa, start temperature of 24.34°C and end temperature of 46.85°C requires 2526 J of energy. Those are the parameters of air that contains 20% more air molecules than the one second rotation of 3.0 L OM617 engine at 4500 rpm. You see the air has far higher pressure difference than 20% (29%), and it is the result of increased temperature of the compressed gas.

The below assumes air density of 1.3kg/m^3

Now to the crazy point. Previous article explained that properly phased suction vacuum is the power behind the resonant oscillations. Maybe you have seen or heard of devices that create vacuum by using compressed air and ejection nozzle. If we make a similar device utilising the exhaust gases we may too be able to make a reasonably strong vacuum source. How should this help us boost air pressure to the engine? We can use it to suck air out of a long tube to make it move at, say 450 km/h speed (125 m/s) and divert part of this moving air by aerodynamic flap or wing to a longer intake tube where the fast flow will slow down to the ordinary suction speed at the expense of being compressed.

The complexity of the design and calculations is high, and benefits are only small, but it is a device with no moving parts and no maintenance. Plus, when properly designed it can be added to existing supercharger designs and to some extent also with certain turbochargers - those which still provide enough power on the turbine output. There won't be many such systems, and those use three turbocompressors in series already ;-)

What am I aiming to achieve then? 20 to 40 kPa boost pressure for the air filer inlet, which would amount roughly to 15-30% more air molecules. Remember that efficiency of this system is much lower than that of the turbocharger, but it has lower delays and you only need to change muffler bearings once in Platonian year.

The last advantage of this exotic boost system is this: past the divisor the flow that leads to the ejector can be equipped with a small tube to let in it diesel fuel to make flames out of the exhaust, or water (or water + something) to make experiments of other kind (like plumes of stink? or even improving emissions!) or glycerine mix to make white or colored smoke trails behind the bike. For many people, that would outweight the former advantages.

How do Ejectors Work?

Very informative air-combustion gas-water vapour gas ejector desigh considerations from 1956.

First thing that will help us understand how much boost we can getis from the Bernoulli equation. That one only takes STEADY, not pulsed flow into consideration - plus, flow of an non-compressible fluid, like water. But still it provides the basic measure - scale. If you enter the values you will be able to see how much is the kinetic energy compared to the energy already stored in the fluid, because air, as we breathe it is already compressed! Comprerssed to about 1 atmosphjere of pressure. The Bernoulli calculator is here.


Post Scriptum: My math tells me this idea is not that practical because due to practical limitations on the size and flow capacity of the exhaust I can forget about a 20% boost. One meter of 6cm diameter pipe flowing 350 L of fresh air per second carries the kinetic energy of 28 Joules. Very modest compared to the 2.5kW requirement I started with at the top. This can only be useful as a sealant of the resonant pressure peak.

Post Post Scriptum: I was mistaken with the statement above, the kinetic energy of the WHOLE mass of 350 L per second is 3486 Joules and that amounts to 3486 Watts. You just need to take care of losing much less in the pipe in aerodynamic friction. Next you will make the pipe long enough to carry just enough energy to hold any counterpressure pulses from the resonator.

Wednesday, June 25, 2008

Tuned airbox design considerations for a modern day car. Tuning the airbox - a two stage idea and computer simulation model. - unfinished yet

This is a hard one. First some links with some math on how to get the resonant frequency of the airbox. What is an airbox? We call the intake pipes with the distributing channels an "airbox". Its purpose is to provide more air with less resistance due to the pressure oscillations driven by engine air suction. Properly designed air intake system can provide 20%-30% power increase over no intake system at all.
It is important to make all parts of the intake well designed and properly tuned to the DESIRED RPM range. 2-cycle engines are the most sensitive to good or bad changes in engine responsiveness and performance to intake system change. (exhaust too, as the petrol-air mix travels to the exhaust, but is then reflected back.)

Also, calculations allow us to understand at which frequency was the original intake system designed, so we may be able to make a completely different hardware design with the same frequency of resonance or at least the same characteristics. In case change the resonant frequency we may be able to estimate how much did we deviate from the original air intake.

Short and easy to understand text written by a motorbike racer, summing the experience and basics behind the operation: (a good starting point text)
http://www.saltmine.org.uk/randy/airboxdesign.html

A very good scientific approach on the topic, using inertia, speed and conservation of energy rules to make the frequency calculation [WARNING units there are NOT consistent, nor are in SI, prease rewrite those constants for your own use, also careful - perharps 2-cycle engines discussed there??]
http://www.calsci.com/motorcycleinfo/Airboxes.html

Next example considers the effect of "cold" air intakes and that they can provide ONLY 3% power increase at 150 MPH on a motorbike, so that the resonant airbox is the main source of power increase.
http://www.thunderproducts.com/AirboxesDynotech.htm

A simple and easy entry in the best physics encyclopedia on the net.
http://hyperphysics.phy-astr.gsu.edu/hbase/waves/cavity.html

Some empirical calculation of an Helmholtz resonator.
http://www.tonmeister.ca/main/textbook/node249.html

In this moto thread the main topic is calculation why the stock air filter may not be that bad idea and some more.
http://www.ducati.ms/forums/showthread.php?t=18854

For anybody interested in some practical examples of intake tuning on sports cars(including 2-stage airboxes)
http://www.autozine.org/technical_school/engine/tech_engine_2.htm


Tuned airbox design considerations for a modern day engine.

And now my own research compilation and writing.

Firtst part deals with explanation of the parts used in the air intake system and manifold, next describes three major groups of tuned air intakes. First (A) consists of long straight pipes connecting engine air intake ports and a common air source. Rather 1960's solution. Next are (B) the Helmholtz-type resonant airboxes that apart of consisting of shorter lenght pipes connecting engine intake ports with a larger volume "airbox". Then we can see even better air intakes, of very complex design, CFD modelled, with many resonance parts, acoustic with superimposed flow, thermoacoustic design. Parts (D) and (E) display some of the well designed air intake systems.

Terminology:

Introduction to electric basics

In electric circuits we have inductors and capacitors. Wirewound inductor does not transfer lot of electric current as you apply voltage to it. It takes time for the current to build up. But when you suddenly interrupt it a spark occurs. You can store energy in an inductor but you can't hold it for long. Next you have a capacitor. Capacitor is very easy to fill up with electric charge and can hold it for long time. But as the capacitor gets charged, the current flowing into it decreases.

With these two components alone you are able to construct a large variety or circuits. The first is LC circuit, the two components in parallel will form a good resonant circuit. Whether you apply or remove current from the circuit an oscillation will occur as the two components will exchange electric charge at the resonant frequency of the circuit. If not periodically fed with changing current supply, the oscillation will gradually cease.

With different LC components connections you will be able not only to make resonant circuits but also filters, low pass and high pass. Low pass allows direct current and slow current changes to be transferred trough the filter while high frequency waves are blocked and high pass filter allows only waves of higher than some frequency to pass while direct current has no effect on the other side.

Compressible fluid mechanics

Aerodynamic equivalents of the above electric components are inertance and compliance. The inductive element, inertance can be made from a narrow tube where gas has to move with high velocity and thus carries energy in a form of quickly moving mass of fluid. The capacitive element is compliance. It is a vessel with large volume where we can store large amounts of air without moving contents of the compliance volume much. The energy can be best stored in a form of pressure increase.

Electric and fluid model differences

Every capacitor has a parasitic inductance. Also, every inductor has a parasitic capacitance. But in power components the differences of the parasitic inductance of capacitor versus the inductance of the inductor is like milion to one. (1000000:1). The same is when we talk about capacitance.
In fluid model you see that the inertance tube has also some volume and that the compliance width is not infinite, common differences are in the range of about 10:1. Also in fluids you can have travelling waves both in compliance and in inertance, but we use those terms to be specific about our intention of what the component will do. So you see that in fluids design it is rather easy to use a single component to achieve some repeatable results in terms of self-resonance. In electric designs we do not usually rely on how much the parasitic value is.
Next large difference is that in simple low-frequency electric components you only have current and voltage to deal with. In fluid dynamics, you not only have a flow with a certain density, flow speed, temperature and pressure. Above that you have also sound speed at which sound waves of the oscillation will propagate. And guess what: all these 5 parameters are interrelated and affect each other! So a perfectly designed air intake system either requires excessive physics knowledce and endless ability to simulate the design on a computer model, or good knowledge and lots of trial and error experimentation or both. The last method is used the most. "Trust, but verify."

What is this all about is to make passive components of air intake system that help the engine to get more air for the internal combustion. We need the air to burn the fuel with and to add to the expanding hot gases. The next part describes the practical implications of the above.

Air intake system designs

A) Inertance only tuned intake
B) Inertance-compliance tuned intake
C) Advanced and multituned inertance-compliance intake
D) example: Honda intake resonator, engine type D16Y7
E) example: Honda intake resonator, D16Y5 and D16Y8 engine types
F) ??? to be written
G)
H)
I)
J)
K)
L) Where did we get the power to compress the air, again?

A) Inertance only tuned intake
Similar to the single straight cut exhaust pipe, typical for many Mercedes and Chrysler cars, the design of the rest of the air intake system is either separate or completely omitted. A short explanation here.

It uses the self-resonance and inertance of an intake manifold pipe, time delay and spring modeled design. Chrysler had it designed to peak at 2800RPM at sixth harmonic. You can surely imagine what the efficiency of a spring-resonant system working on 6th harmonic is. Example of realisation of the 77cm intake in the Chysler on the right.
[Explanation: imagine a pendulum of a clock. It swings to left and right in one second. So you swing it and on sixth swing you use the energy still remaining in the pendulum in its peak height. Not a problem for a clock pendulum, but if you swing a garden hammock you will notice the swing amplitude decays quickly. Plus part of the pressure pulse does exit the pipe and is not recovered back. Next design step takes care of that.]

B) Inertance-compliance tuned intake
This is a smarter design in the efficiency, no need to resort to 6th harmonic [ed. note: eww], it works in a similar way: the flow of the air that is flowing to the engine is abruptly stopped, so as a result the flow ceases and the energy of the inertia is converted to a pressure increase. What do we do now? We obediently return the resulting wave ripple back to the sender. But as it exits the relatively narrow inertance pipe it discovers wide and open space where its energy can be safely stored with little losses. So this wave travels trough the compliance volume to the other side where it either bouces back or finds the other inertance tube where it compresses the air. In this mode it acts much like an Helmholtz resonator. All four-cylinder motorbikes use this type af air intake. The good point about the design is that you can use simple shapes (square shapes of a box and single diameter pipes) to get good results. Also, the design and calculations are well predictable.

Remember that while some people anxiously try to minimise losses and save amazing hundreds of pascals (say decreased the pressure loss by 400Pa) the resonant system is all about making the pressure to go up and down periodically until it achieves amplitude up to 5-10% or more. 5% amplitude means 5% of the surrounding air pressure, that is 101.325kPa; 5% is then 5000Pa over and under surrounding air pressure in the peaks. So you see that our design goal is not to minimise the pressure loss, since the gains are small, but making the amplitude high and in correct phase of the air flow with suction in the engine intake ports. Yes, it needs to provide the pressure at the correct time AT the intake port, what pressure and when they occur elsewhere in the air intake system we don't care that much. Conclusion: you can reduce whirl losses later, once you have a working resonator.

C) Advanced and multituned inertance-compliance intake

We can do more than tuning the intake manifold only. It would be really naive to think that once you have intake manifold with good resonance that the resonating pulses will just stay there. In fact, you can observe at some engines that the air is being expelled out of the intake itself! So the pressure wave we so hard tried to build cheaply escaped from being useful to us. We can do two things to correct that. One is to make sure the pressure wave has no easy way of escaping the compliance fox of the manifold (the airbox), the other is to use the escaping pressure wave to promote further resonance of the air intake system as whole. And as you already can imagine, it is not possible, nor meaningful to completely containg the resonant pressure in the airbox, so both principles will be used. Parts (D) and (E) show one such system where the air intake system as a whole is about the same volume as the engine itself!

On a side note: Honda car engines typically perform at 100HP/1L of displacement as stock sold.

D) example: Honda intake resonator, engine type D16Y7

It doesn't surprise that to make a small engine with high power you need to be efficient and effective and that the Honda design again is. If you look at the size of the air intake components you will see that compared to the engine size, it is enormous. By "Effective" I mean "it does work" and also that it has good operational principles. I would like to point your attention to the fact that the pipes there do have their endings abrupt or rounded exactly according to the purpose they have! Some people would like to have round edges and large diameters on everything. Wrong. Even the small pipe leading to the front compliance volume with straight cut ending has its purpose. It forms a separate Helmholtz resonator, plus the separator in the middle also makes the resonance properties better (I think it is there to extend the resonant frequency). The pipe ending that leads to the air filter also serves as a gas diode, it allows the gas flow go one way easily and the other way is much more restricted. If you count with me you see 4 inertances, 2 compliances, and 1 double compliance box and 2 turns. Out of this the intake manifold is only 1 inertance and 1 compliance. See the difference of this complex air intake design and the simple long tube design from the 1960's Chrysler?

E) example: Honda intake resonator, D16Y5 and D16Y8 engine types

This intake system has a simpler compliance/helmholtz resonator on the air intake, but you can see something interesting in the straight piping right after the air filter in the schematic diagram. It looks much like a load cell to me. If it is a load cell it may be there to limit the maximum amplitude of the resonance; That alone leads to the decrease of the Q factor which in turn widens the resonance frequency peak. It may also serve as a separate resonator to buffer the sound pressure wave returning back to the air filter to protect it from high frequency vibration.





F) Optimal resonator, Optimal piston suction diagram.
2-piston compressor, wave pattern


G) Choice of resonance designs depending on engine design.

From a technical design standpoint we can put resonator designs into two categories: pipe-to-wall resonator and pipe-to-pipe resonator. It is not exact name, but you understand it when you see one.

Pipe-to-pipe resonator inertance tubes are not in the same phase of the resonant box. The opposed pistons compressor air resonator is a typical pipe-to-pipe resonator, pulse from one inertance travels trough compliance to the other inertance. This design however can only be applied in systems where it is physically possible, it is also not applicable to 3-cylinder engines too! Advantage: the oscillation is driven two times per one cycle, and each pressure pulse fed into half of the total number of inertances. As you can calculate the volume of the compliance and inertances of your design you will see that it makes a big difference.

Pipe-to-wall resonator inertance tubes are in-phase. Engines with suction ports in regular intervals are typical candidates for this type of design, also space constraints many times do not allow to apply other designs (motorbikes, cars). Disadvantage: since all inertance tubes are in the same phase, they load the compliance resonance more, also pulse is distributed among all at the same time, but only one of them has advantage of it, and per resonant cycle only one inertance tube can promote the resonance.


Volumetric efficiency?

I prefer only measuring how much mass of fresh air we managed to entrap in the compression volume. Consider that the whole volume enclosed by piston, cylinder liner and head is MORE than the displacement volume. So, should we count 100% VE as mass of air that would will the displacement volume and the volume in head cavity, piston cavity and prechamber at 101.325kPa and 23°C? Plus, if we manage to get inside some frozen air in cubes and double the total air mass entering combustion, would it be 200% volume efficiency? Therefore, lets understand that we need and want to know the total mass (weight) of fresh air we manage to use for the combustion process. Also, "volumetric efficiency" of 90% and 110% can mean the same amount of air molecules, depending on the conditions.

H) Stock Mercedes example, Suction pattern, loss analysis

hypothetical airbox1
- the good and bad points of this design become obvious
Good points: the low height compliance volume works more like a waveguide and indeed we can predict wave propagation inside of it in 2D simulation well. We can also see how a sound wave propagation would go if we use a vessel of the same shape and fill with water. A droplet of water in one corner will show how a sound wave will travel across such a rectangular box. That is a great advantage of these 2.5D manifolds.

Minimising pressure runaway back to the air intake and air filter
Hypothetical airbox2, improvement obvious, resonance
Improvement 2






Straight inertance to intake port with rounded edges: rounding edges causes little widening frequency response, small change in the base frequency, less static air drag, slightly decreased impedance and tiny bit increased parasitic volume of the inertance. Suzuki uses this system as their manifold is of constant internal diameter and maximum amplitude of the resonance is very important - motorbikes use mostly high RPM operation in narrow range.

Horn-shaped inertance to intake port: tapering the inertance tube so that the diameter is narrowed or widened at an angle. This causes things to be complicated. While it is predictable what it will do with static air flow, with pulsed flow it has the following effects: increase of the parasiti volume in the inertance, better potential to compress air at the narrower end, but it easily escapes due to the same reason, the resonance is much wider due to the interference and reflection from the steeped wall surface and also of lower amplitude compared to simple straight pipes. Despite the ugly disadvantages when inproperly applied, they have their place, ideally as straight air intake where each intake port has its own "horn" to surrounding air without filter. Per unit of intake manifold weight this is the best solution.

Relationship between inertance and compliance in an intake manifold
From the above you see that sometimes the design leads you to a point where you create a manifold which has long, wide pipes connected in parallel, equal distances to a box of small volume.
Not a problem by itself but consider this: it 1) decreases the maximum amplitude of resonance you are able to achieve, 2) even the pulse you manage to make you equally distribute among say all four pipes, thus minimising the resonance benefits and 3) all changes in diameter cause energy dissipation by converting one form of stored energy to another.

Flow rules.

a) If you have a flow of fluid trough narrowing passage, two things can happen: either it passes at the end with increased velocity at the same pressure as before, or the pressure at the end increases while the flow speed remains. [Very simplified, usually part of both happens and also temperature changes too!]
b) Plus, if you manage to increase the pressure by suddenly obstructing a flow of a fluid, a sound wave of this event will get reflected back and the flow will slowly revert due to the obstruction and due to the fact of the higher pressure. You may have noticed in your house that when you suddenly stop large flow of water, the pipes will make a "tikk" sound and also that the overpressure protective valve will let some water go.
c) With air, we are interested in these parameters of air in front of the intake valve: pressure (density), speed, direction of movement. We want all three to have right at the same time. I hope you already understood why and what can go wrong.
d) Conversion of energy forms is less than 100% efficient. Having horn-shaped inertance pipes may help air compression and low flow resistance, but at the same time it impairs resonance amplitude and introduces new losses from multiple flow conversions. Therefore, use with geat care and consideration!
e) with the point d) clear you have to ask yourself: "do I want to make a wave or do I want to make a flow?" - ask yourself honestly: "what is the mean flow speed and what resonance amplitude am I going to see?" As the flow speed increases the resonance makes much more sense, but at the same time the aerodynamic flow restrictions increase too. Don't overdo one and don't forget the other!

dalej: opisat priklad mercedesu, jednoducheho Mercedes Helmholtza, vylepsit ho o rozsirenie
uviest priklad sania ktore by sme chceli pre idealny rezonator (dvojvalec), sinus, a realny stav stvorvalca opisat rozdiel v umiestneni sacieho potrubia ako daleko od seba -> protilahle potrubie vs. protilahla stena -> rezonancia v polvlnnom mode a v celovlnnom mode
Realny saci diagram a rezonancia na n-ty piest. (stale hovorime o zakladnej frekvencii!)

It is a design that tries to build high pressure, but fails to contain it as it easily escapes to the air filter as the compliance diameter is about the same as the air inlet diameter.


Notice that we did NOT change the frequency of the resonant box, neither did we desperadely use n-th harmonic frequency, we still operate the resonator at its efficient, fundamental frequency and the only thing that changes is the piston that catches the next resonant wave. Isn't life great? Thus the problem we originally had with the resonant frequency selection solved itself. Well, at least partially.

* tuning intake with a turbo? *turbo and supercharger separation *overlapping valves and turbo
*invention-turbo with external valve *zmena casovania so zmenou plniaceho tlaku

[B]As for the air intake:[/B] to sip 600ccm of air trough, say 8 square centimeters area in 10 miliseconds, you need the air to be moving at some 75 centimeters per second. Phasing of a small compliance (volume) and large inertance (long pipe from engine to airbox volume) is different than of large compliance and small inertance even at the same resonant frequency design. In other words if you make a new airbox with different resonant frequency, you can still have at some RPM the very same phasing and performance as you did originally!

The stock intake is more like pure inertance design, so that at higher RPM the wave might not be even reflected back to the volume, so that no or less standing wave resonance could occur at high frequencies there, and it would be of less meaning since the intake lines are already long. This is not good, nor bad! It is a design choice for optimising distributed interrupted flow. It is good for making steady flow at the input, but it doesn't utilize compression sound waves very much. (to tell the truth, it does resonate but the low compliance volume causes such terrible Q of the resonance that one is led to believe the designers intended to make it quieter rather than a racing car.

Now if we have a look at the 13x6x2 inch box: the air inlet is not even streamlined, and that is the point. The area behind the air inlet tho the wall forms a volume that has little superimposed flow and gladly acts as a pressure buffer, also, the wave caused by the suction forms in a plane parallel to all other suction ports and perpendicular to air inlet.

Also, the extended suction hose (black plastic) is a complementing point: if you lowered frequency of the airbox, lowering the resonant frequency of the hose+air filter also makes sense. Plus, in my opinion, the stock air hose is rather short and could use a higher inertance than it has. (there is significant pulsing of air intake there at low RPM, try your hand or smoke or flame to see - it does blow air out! (not only sucks).

In my design, I would love to use gas diodes. LOTS of gas diodes, as I outlined in my airbox design thread.

The stock air intake just looks much like the intakes of old 1.2L 60HP petrol engines here. And guess, the OM617 without turbo is too a similar powered engine :).

As for any airflow design: it is really true that you make calculations, assumptions and design and make five, six, seven, eight, nine, ten variants to see which performs better. Sometimes those 5% additions count. The computation is NOT easy, as I have yet to find any useable CFD simulation software capable of simulating *COMPRESSIBLE* fluids -> gases. Fow water simulation is lots of software available. Recently (late 2007), Boeing or some other company used one of the most powerful supercomputers on the planet (BG/L platform don't remember ranking, from 1 to 3) to simulate just some segments of the burners in a jet engine. Not whole engine, not complete burners, just some of it. And it took some time too!

Where are the times when I made a perfect electronic design and assumed it would just work? :D

In fact the link it points to http://www.chrysler300club.com/uniq/.../ramtheory.htm talks just about what I said above: a pure inertance inlet design. That is nice, but not the best. And that is just the design stock OM615, OM616, OM617 uses. The purely inertance designed intake is only resonant in the pipe connecting the engine suction to the airbox. Other sound power is wasted and - as I said before, running n-th harmonic resonance is inefficient too.

The speakerbox design all racing and street racing motorbikes use is the latest and most powerful air intake design. It does not rely on purely making more air available due to the pure inertance of the moving gas, but uses a comliance, a volume where to store the energy from the wave for a much, much longer time than it is possible in a reasonably long inlet pipe.

Actually the site proves one point: we need to increase the inertance or to provide gas diodes on the outside air suction pipe. A 2-meter long pipe to the air filter actually makes sense! WoW.


Where do get power to make the "compressed air" from?

You may want to ask: where does the power to make "compressed air" out of nothing come from? Good question. In an engine with non-overlapping exhaust and intake valves the power comes from the motion of the piston which cause the air to be sucked inside. More specifically it is the energy needed to make low air pressure in the piston volume which gets the mass of air into motion. For this reason the inlet pipe to the intake valve needs to temporarily provide resistance, and this is what the inductive coils do, but in our case of using air it is called an inertance. But as you can see the purely piston driven intake airbox resonator has the disadvantage of unfortunate timing and low rate of change. Sometimes you can see it corrected by opening the intake valve late, when the piston is well on its way down.

Overlapping valves - by that we mean that the exuast valve is still at least partially open while the intake valve opens. Understand that this happens in motion and at high speeds, so what it does cause is a draft. While the exhaust gases have been set in a very fast motion, also the exhaust pipe is long, it acts as a system with very high inertance that has already been set into motion. Where this system can be used: racing cars, motorbikes where emissions are not a problem, fuel injected engines, including diesels. :)
Note that this actually sets the air in front of the intake valve into motion faster and sooner than would the purely piston driven mechanism do, also the total energy invested into pumping/sucking the air can easily be greater, showing promise of higher air induction. And you can be sure that street bikes, etc use it at lot in their 2000-15000RPM range. Oh, did you note how this affects the exhaust sytem design? making the exhaust pipe too short, too wide or narrow would all decrease the inertance effect driving the air boost later. Now remember, we need the air to burn more fuel. Burning fuel into carbon and hydrogen is the least efficient thing we can do.



Exhaust:

We will sort the exhaust manifolds in 4-cylinder engines into these categories:

1) All 4 exhaust ports connected very shortly into one pipe. This is typically used on non-overlapping exhaust and intake valves where the joined exhaust port feeds a turbo. Racing unfriendly and if used on normally aspirated engine a bad idea.

2) exhaust manifold with all 4 exhaust ports are connected with equal lenght pipes into a common exhaust pipe. This is the case of most stock exhaust manifolds. Nothing extraordinary. Just the bare stock. Car manufacturers use it also because the manifold can be made by sand casting of cast iron.

3) exhaust manifold "4-1" - The basic racing choice, you have four equal lenght pipes from the engine exhaust ports connected at the end into common exhaust pipe. The four pipes are long, rather straight with only the necessary turns, with diameter and lenght specifically selected for the engine, camshaft and RPM range.

4) exhaust manifold "4-2-1" - The best racing choice. Similar as above, but the ***finish here*** Properly choosing all six parameters (diameter, lenght) is not a trivial thing to design, some empiric experience and lots of calculation help. Web calc.

5) exhaust manifold "straight pipe for each exhaust port" - each exhaust port is equipped with a separate pipe, each of equal lenght and diameter. Usually straight. This is obviously a loud solution, and not always has only advantages over 4-2-1 configuration. But sometimes there is no other option, like with extreme engine displacements and/or extreme power levels (1000kW-8000kW). This simplest design can be even further improved by correctly using the entropy levels of the exhaust gases like in NASCAR exhausts (not discussed here).

Interrupted flow is bad idea

No matter how slow the fluid flow is or what the internal pipe diameter is, getting the fluid to move and stopping it is like moving and stopping a train.
1) you need energy to get it moving
2) when you get it moving at constant speed it is only the aerodynamic drag you spend power into
3A) when you try to abruptly stop it (by an obstacle) it either compresses the obstacle or the train or both
3B) while moving, it has inertia that can be used to either push or pull other trains.

Case 3B application: exhaust manifold. What 4-2-1 exhaust manifold does is that as one train leaves the station 1 it just catches the last bandwagon of the train that left before from station 2. It does not not crash into it (and thus slow down), they simply join into one train. Similar thing happens as these two trains join the extended train departing from stations 3 and 4. [[I cheated a bit in this example]]


The reason we do it

When you have a pulsed fluid flow; especially compressible fluid like air or exhaust gases; you have to remember that when you start pushing the fluid into a pipe everything goes fine until the flow finds an obstacle which includes diameter change and pipe end. As that happens a sound wave is reflected back. Did ...Imeant the pressure frontwave

I don't have an easy to understand example, the easiest example is the exhaust of a 2-cycle engine. If you don't know how it works use this approximation. Take a glass bottle. Put it under ... and .. water to fill it rapidly. as the bottle will get filled the water will suddenly strike high into the air, but after that the flow will be again smooth..

If you have read it this far, please leave a comment so I have a guestbook here. Thanks.

"Anodised" aluminium, alumina over aluminum pistons

Friction. Friction is bad for engine performance. Aluminium piston in cast iron liner is a relatively long lasting and low friction combination.Aluminium puston in straight aluminium cylinder is a bad idea. Dies fast.

What is usually done is coating, like iron coated alu piston in alu cylinder (Porsche), or better solution, nikasil, kanigen or similar coating in the cylinder and alu piston.

These solutions are good, but technologically complex and not easy to implement for a hobbyist racer.

Mechanical watches of the past used texts like "17 jewels", what that meant there were 17 bearings consisting of ruby or sapphire. And indeed, steel over ruby or sapphire forms a very good bearing. Sapphire (and ruby) are minerals which re Al2O3, aluminium oxide. Guess what! Pistons are mostly from aluminium!

What can be done is that you can make the sapphire-like coating over most aluminium pistons! Standar method is anodic process where the aluminium part is submerded into sulphuric acid (H2SO4) or oxalic acid (in my opinion far better for this purpose!!) and you turn on the voltage source for several hours. The result is a aluminium oxide coating that is somewhat porous (and this may help us) and should copy original alu surface. The problem is mostly in thickness achieved: it is small, micrometers, maybe up to 10, 20. Next problems is dimension change: the aluminium oxide CAN be cissolved in the acid too, so sometimes after the maximum thickness is achieved, new aluminium oxide is created only at the expense of dissolving some of the top layer.

In any case, the piston surface must be very smoothly polished to be of benefit to us. Sapphire is hard substance and any loose aluminium oxide would only serve as an abrasive. While still on the aluminium piston, it can be a very helpful ally, and while OFF the surface a very nasty enemy. So the mechanical surface preparation is of the most importance to us. Also, manu aluminium alloys can not be anodised! The last point is that the Mercedes pistons use steel inserts which don't like oxidising in acid at all, the steel surface would need to be well protected from the bath and fumes!

INVENTION: Caustic "anodising" aluminium oxidation process

I did that some years ago. Basic compound in the electrolyte is water and caustic soda. Yes, the very same caustic soda that dissolves aluminium and attacks aluminium oxide on its surface. However we can stop that process by applying electric current. I folgot the current density needed, but it was very high, optimal (for quality) temperature was 91°c-93°C, the bath also contained some dissolved aluminium in the process, clean fresh bath was a lower uuality producer. The other electrode was stainless steel. Lots of bubbling, bath temperature is kept by the current alone. One more point: I forgot which electrode was "+" and which "-" pole, it may not even be an anodising process then!

Disadvantages: The part diameter will be less than it was at the start of the process. Some aluminium alloys will totally spoil the bath.

Advantages: Many, it needs some observation, but it is very quick. The resultant coating is transparent, shiny with milky-white look. Very slick surface after the process depending on bath state can have high environmental resistance (TESTED! some of them were thrown out on ground, in contact with soil, rain and all the dirt you can get). After applying oil, the surface is oleophilic (attracts oil, yup, we want that!) and the friction factor on the surface drops a lot too. The material used were forged aluminium spoons and the surface of the later bath specimens had milky pearl-like look and after oiling kept incredibly slick surface due to the oil filled the pores.


INVENTION: Use elecroless ""anodising"" process

And now for something I do in the recent two days. I made a path and submerged a slightly worn aluminium piston. I cleaned and degreased it with acetone. Surface was polished with 6-micron SiC powder which also removed contaminants and aluminium oxide. After dipping the piston in the bath (some hours), a coating of grayish metallic color became evident in all exposed aluminium parts. The coating is hard and slick when tested with fingernail, not up to the slickness of the electrolytic coating above, but the thickness is also very thin. (it gets better as the coating gets thicker)

Maing ingredients besides water are two neutral organic compounds and a minority of some salts (weakly caustic). So far I could explain it only as that the compunds serve as an oxygen transfer agent, as I used tap water, and the sodium ions attack the aluminium to form hydroxide which gets mostly converted into aluminium oxide. (Aluminium hydroxide would cause the gray coloring for example). The two organic compounds would serve as an oxygen transfer helper, the aluminium itself acts as a catalyst for the reaction and the organic compounds propably help during the oxide formation to promote the formation of nanopores trough which the reaction is able to continue further down into the metal. To prove this hypothesis a presuurised container would have to be used and filled with air, say ordinary compressed at 10 bar (~11x the pressure we breathe) would be a good start. So far, I was adjusting the bath and the coating is thicker, slicker and darker. As a side note: with one liter of air you can turn 0.16g af aluminium into oxide (quick math, take care).

P.S. I am already improving the process, the result so far looks like a very slick colorless transparent sapphire!

Wednesday, May 21, 2008

Night drive in a Mercedes W210, very fast and really colorful.

You have to hate youtube for the recompression that the Youtube forcibly does on ANY video file (including the one that is precisely to their specifications in bitrate, resolution and codec.



The front windsield glass was dirty and needed cleaning, also the car could use a bit of car wax and some polishing too.

Labels:

Friday, March 07, 2008

First a boring brief summary of what is bad for combustion, processes which form carbon and we can usually see black smoke:

1) lots of fuel with little air to circulate with at high temperature (1000K and more, air is not where the fuel is and vice versa)
2) fuel spending too much time in a zone with extreme temperatures without oxidiser (oxygen) or reducer (pyrolysis and carbonisation)
3) bad fuel dispersion so that fuel particles form a very rich mix with little air to burn with. (low droplet speed, large droplets, etc.)
4) ...

Now interesting summary of bad combustion forming white smoke:
1) fuel that is injected too late, has little time to ignite and combustion starts late
2) fuel that ignites too late due to its chemical properties, or much lower speed of sound of the liquid (foamed, emulsion)
3) fuel which needs high temperatures to burn properly but does not instantly give out enough heat to support that (water rich emulsion, improper chemical composition)
4) fuel which can only burn slowly so that the flame and combustion ceases prematurely due to pressure/temperature drop at expansion. (bitumen burns slowly, yet ocean ships have lots of it in fuel, 100RPM engines don't care)
5) fuel which contains inert material (metals, etc.) which form condensate during gas cooling

Pyrolysis is decomposition by heat without the presence of oxygen; forms carbon and combustile gases, gasification is decomposition of substance by heat with the presence of some oxygen, its aim is to make combustile gases only. And that is the aim of prechamber design - to convert liquid fuel into preheated, easily combustile, easily flammable combustile gases or mix with dispersed fuel droplets.

Thursday, March 06, 2008

Prechamber with heart insert - function and description

This is the classical prechamber used in Mercedes diesel engines. So, let's come with some pictures and description.. and important part here will be the injector operation and optimal (dream) setting. But let us first have a look at some basic physical law that we have to take into account which basically states that the bounce-off angle, or reflection is the same as the impact angle. This is true for light, for solid elastic objects it is almost correct and for newtonian fluids - we can at least take it as a rough approximation valid at some range of impact angles, drop size and impact velocities. Here is the diagram:

You get the picture.

And now we get to why we should think about it a little.


Now to the real thing. Let us have a look at the nozzle - prechamber heart insert configuration. First the nozzle. First figure depicts fuel spray. There is a deaf zone in the center - at least it should be, so that no droplets, or even streaks are aiming directly at the heart of the prechamber. This would only cause the droplets do disintegrate, vaporize and oversaturate the area in front of the nozzle with fuel vapours and droplets that lost speed and are just waiting for a disaster. The "disaster" is that there is no flame, just well dispersed fuel that has little possibility to combust fluently, it just accumulated and accidentally ignites all at once later. Properly, we would like the fuel to form one long continuous flame ejecting out of the prechamber to the main area between the head and the piston. Well, this can be helped. [* some nozzles eject a tiny stream directly onto the heart, but it is really small amount and velocity, plus the microdrilled hole plugs itself later anyway]

[the second image is how the spray goes around the perimeter of the insert, the third is a magnification]

IF, the fuel spray goes just around the prechamber insert, and IF it only lightly touches, not only the droplet does not lose all kinetic energy, it also is able to continue in the supposed direction forward. The ideal "travel plan" is this: The droplet starts its travel leaving the nozzle at original speed, this rapidly drops down as the droplet loses much of its kinetic energy, also loses some weight due to evaporation, but not as much for the short travel distance when it meets the prechamber heart side and does a touch like a tennis ball on a court. The prechamer heart is already glowing red hot. The droplet evaporates either entirely or from large part and the vapour ignites. In case of droplets flying by, or those who do a touch and continue in forward direction, leaving with a flaming tail behind them (see BOSCH literature). [overly simplified since the spray is dense and one droplet does not travel alone but I think the above illustrates the function well]

In diesel engine we want a long, constant pressure combustion, which could be achieved by one, long lasting flame source - but fuel ignition speed is limited (1-2ms or so), plus one type of fuel can burn at different rate at different pressure, temperature and droplet distribution. The problem is that the combustion itself is what primarily changes the pressure and temperature. So if you get a bad start, you will not correct it later. With the prechamer insert removed, you get a hard nailing sound from the engine. This is caused by spontaneous ignition of large amount of fuel and further resonance - and lots of loud fenomens happen - basically, spark ignition engines work in this way.

The heart shape: when the insert is worn in a way that the middle part is not bulged out, but flat, hard, nailing combustion also mostly occurs - so it can be seen that some of the droplet stream flows around that direction too, plus, a flat center would cause large aerodynamic drag, sucking the sream to the center and behind the insert deflecting fuel droplet stream too much due to aerodynamic drag change. (well, all flow inside prechamber changes with one component aerodynamic coefficient change)

Also, remember, streams flowing at the proper angle around an object tend to bend BEHIND that object, and in this case it would really help the combustion in the right direction. In fact, if this is propably the most important aspect: the prechamber heart insert can be considered an aerodynamic insert that has the right shape to deflect the stream flowing around it so that the fuel stream aims directly at the prechamber exit. [you saw a flow around a wing, the flow lines close behind it]

For those of you who are reading this this far: Example is an OM617 engine which has some hard, nailing sound and lots of black smoke when new DN0SD265 nozzles are used in injectors set up at 150BAR. AT OM601 and OM603 engine it was tried and proved that pressures over 145BAR too cause very unpleasant combustion noise. For the mentioned OM617, lowering injection pressure to 138BAR caused the engine to be as quiet as a sleeping baby. We here used 135BAR or 130BAR in different cases to the same results, depending on the diesel grade the engine could be as quiet that at idle the loudest noise were the valve springs, and that is a lovely sound! (you know, such "yumyumyumyumyumyumyumyum" sound)

The nozzle opening pressure can change the spray angle and distribution a little, but it mainly and radically changes the droplet exit speed. (we consider some constant pressure loss in the injector assembly since the injectors are fed with piston pump). More on that and on pV diagrams later.

Missing letters? diagrams? explanations? grammar? leave a comment.

Friday, January 11, 2008

Death involving knitting accidents on the rise! Pure scientific proof!

I hate to say that, but there is rapidly increasing number of people who died recently in knitting accidents! Specifically from around 7 to aroun 122 at 20:00 CET, January 11th, 2008. This is a horryfying fact! We must act! We must act now AGAINST death caused by knitting accidents! While I am alarmed at the rates of dying in knitting accidents have risen up recently, the number of reported deaths in blogging accidents has risen from about TWO to around 2440 at 20:10 CET on January 11, 2008. That is a very sharp increase, which can not be explained by any other way than the bloggers just became crazed with a new, unsafe, unproved method of blogging.

Surprisingly, here come the other data too:
Before --> after
ice skating: 94 --> 4 [hate to say that, but the ice has probably melted and this could have resulted in more people sitting at home and doing nothing or blogging]

gardening: 100 --> 119

camping: 166 --> 166

skateboarding: 473 --> 478

surfing: 496 --> 502

elevator: 575 --> 68 or 609 (using "an elevator" yields 609, "a elevator" 68)

skydiving: 710 --> 813

Here this scientific site has a graph of how it looked before and how it looks now you can google for yourself!

Monday, November 12, 2007

English (Flinstone) to metric (SI) conversion table

Follow this link or read below, amazing work guys!

English Unit

Quantity

Multiply by

Metric Unit

inch

1

25.4

mm

foot

1

0.3048

m

in2

1

645.16

mm2

ft2

1

0.09290304

m2

ft3/min

1

0.0004719

m3/s

BTU/hr

1

0.2930711

W

BTU/hr-ft-F

1

1.729577

W/m-K

BTU/hr-ft2

1

3.1546

W/m2

BTU/hr-ft2-F

1

5.67826

W/m2-K

BTU-in/hr-ft2-F

1

0.144228

W/m-K

F-ft2-hr/BTU-in

1

6.9333466

m-K/W

F-ft2-hr/BTU

1

0.176109

m2-K/W

lbf/ft3

1

16.01846

kg/m3

lbf/ft2

1

47.88026

Pa

mph

1

0.44704

m/s

Sunday, October 14, 2007

Again one injector post

This time again for the AN injection. Well The ADN (Ammonium dinitramid) looks nice, but it is considered unavailable. Both technically and financially. The CAN (Ceric ammonium nitrate) has a melting point of about 108°C, so it could make a very nice alloy with the AN. Especially for its high reactivity with organic compounds.

Back to the injector or spray. One site here summarizes about all the injector nozzle types I have considered so far.

"Atomizer designs include co-axial air assist, liquid and air swirl, pizo-electric induced fluctuations, effervescent bubble atomization, rotating cup and disk. Electrostatic charging of droplets allows deflection of droplets in flight and avoidance of deposition on surfaces"

Well I did not consider electrostatics in helping the dreaded AN crust problem. Some possible solution is to lay the omega chamber in the piston with thermally insulating catalytic material, so that the AN could be deposited and boiled off and decomposed in case it comes in direct contact.

Tuesday, October 09, 2007

In reply to a question: What is the effect of cerium oxide to fuel?

I recently answered to the question on wikianswers

What is the effect of cerium oxide to fuel?

Short answer is: none. At ordinary room temperatures is the ceric oxide powder rather inert. It has the potential to oxidise various other chemicals and materials, reduce nitrogen oxides for example, but you will not see any measurable effects in room temperature.

The cerium oxide is inert. The point when it becomes interesting is at higher temperatures when it can oxidize carbon for example at temperature much lower than the carbon will usually burn. Another useful property is that it will reduce nitrogen oxides and take the oxygen to form its ceric oxide state. This is used in car catalysts due to good efficiency and favorable price. Yet another use - which can be derived from wikipedia information already is chemical reaction with laughing gas - N2O to form really strong, orange oxidiser (NH4)2Ce(NO3)6 - ceric ammonium nitrate. I plan to test it in a rocket engine fuel soon.

Just to note - many combustion processes, whether in furnace, cars, rockets can not be enhanced, taken more power from them, because of the limited speed of reaction. That is where catalysts take place. Ceric oxide can act as a catalyst. When reacted with certain nitrous oxides it can take form of another chemical composition which acts as a strong oxidiser potentially increasing the speed of the reaction even further.

It is said that the east german racers used ceric oxide fuel additive to improve combustion of their vehicles on some races and thus cheated, but closer information on their setup is hard to find. In general ceric oxide will improve combustion if the combustion has tendency to form carbon particles, like in diesel engines or race engines with high fuel:air ratio.

The maximum surface area of ceric oxide nano-powders ranges from 35-70 square meters per gram of the powder. Ordinary polishing powders do not have such large surface area since they are aimed for polishing, not as a catalyst.

Sunday, September 16, 2007

Motor oil aging, wear and consideration when to change it.

As I was thinking how to explain the aging and some important parameters of a motor oil, I came to two interesting links which I must post here.

The first is about measuring the reserve alkalinity which is important because it shows how much detergent the oil still is (1. blocks the formation of bigger carbon aggregates and 2. neutralizes any acidic compounds from combustion and burned oil itself) and you can see the rapidly increasing wear when they are depleted here.

The second is how to interpret the parameters of the oil. You can start reading at Oxidation, then following the AN/BN (acid number, base number) explanation. This helps to have in mind when comparing the BN (reserve alkalinity) in an oil, plus the Sulfated ash. There are some new oils which are low in ash, but still have high reserve alkalinity.

A worn engine would like to have oil with high BN number and still low in ash and good viscosity (not very low).

The reason behind this is: Since the blow-by sprays the oil into fine mist which is then burned by the engine - you need low ash oil. (all modern oils are low-ash, well the very new API-CJ is even half of that! :D)
You need high reserve alkalinity to neutralize all the trapped acidic gases that blow-by the piston rings, plus you need to wash and disperse increased amount of soot. Plus there is this burned oil mist that you partially need to wash too. (It can behave as a weak acid.)
More viscous oils are not that easy to spray, so the more viscosity an oil has at HIGH temperatures the less of the oil is likely to be sprayed into a fine mist. But the low temperature viscosity has to stay adequately LOW, because you still need to cool the oil and you need to start in a cold winter too.
The fourth thing to be taken into consideration is the price... a Fully syntetic diesel motor oil of viscosity SAE 20W-50 MB228.5 would be lovely, but the price is not!

More ideas maybe later.

for my Mercedes friends, more links.

Some site with Mercedes oil specs explanation.
some more later...

and finally, my private motor oil explanation, some table with available oils to me with pricing and explanation of what is what... English verion as time/donating permits.
SHPD, UHPD motor oils

Saturday, August 25, 2007

Oxidation and fuel combustion burning catalyst

There is a good catalyst for diesel fuels which supports complete burning and what more, it works better in environment containing water vapour, and even better for us, it consumes (reduces) any nitrogen oxides it finds! It is Ceric Oxide CeO2.

It can be bought in industrial quantities in China and in Canada, the Canadians have few interesting things, like Ceric oxide with Surface area = 70-90 m3/g - or even better nanometric powder with particle pize: D50 = 10~100 nm. That surely is interesting.

The chinese site has Ceric Oxide ground for optical glass polishing, like CERIMAX 1003 - 0.6-5.0 micron powder or even better (it's not that bad to be used in certain nozzle types) .

What could be interesting is Cerium Chloride. Cerium requires only low activation energy for most reactions, like 150-250°C and Cerium Chloride is soluble in water. I thing that mixing Cerium chloride with ammonium nitrate could lead to rapid decomposition and perharps a detonation even at low total mass of the nitrate. You should be very careful and wash your hands before working with ammonium nitrate not to bring even Cerium traces into it! The last thing you could possibly want is to have ammonium nitrate that has a tendency to decompose!

In USA you can buy Ceric oxide here, as a polishing agent, price 49$ per kilogram! If you want ceric oxide particles of the right size and premixed into diesel fuel, buy ENVIROX which is designed exactly for use in diesel fuels.

In Europe, you canj buy Cerium oxide at UKGE they are rather cheap and have other polishing and grinding media too. I can recommend anyone to view the annopowders under microscopes here at Kemco International as they have some very fine catalyst powder with bulk density of 0.25grams/cm3! That is 28.4 times less than solid a piece. Surface area is 55 - 95 m2/g among the highest. Their complete nanomaterials list is here. [a note: imagine a small glass full of this powder - only 3.5% of it is the ceric oxide, the rest is air. If you pour fuel over it, you get close to 100% 'coverage' with only 3.5% of CeO2 content by volume. It means the aggregates have good distribution of their active surface, not located in certain 'hotspots'. When properly used, this kind of catalyst may prove the most effective one, because it is most evenly distributed. High-temperature gasoline engines which produce a lot of nitrous oxides would be happy to have this catalyst in their fuel. Well, the DDR (East Germany of communist era) used them (illegally?) in their racing cars and won some competitions too :) Not sure if they used any nano-technology as we call it today, but just a little catalyst adds a lot in efficiency.]

The last company to mention is NanoScale, their Ceric oxide is here. It is not as perfect catalyst as the one from Kemco, but they have a complete pricelist online and you can order directly with a credit card! They ARE costly but it is nice to have 500 square meters of surface area in one gram of TiO2!

Another nanoparticle 'megashop': NanoArmor, great catalog.

Did I forget Engis(uk) Ltd? Oh yeah, the offer the finest non-nano ceric oxide polishing powder. It is Unicer 636 - You have to contact them by e-mail here, they sell it in 1 or 25kg packings. The Unicer 636 has "AVERAGE PARTICLE SIZE 0.6 – 0.7 μm". This is good for forming polishing slurries, because the powder does not separate fast, or at all. For mixing into liquid fuels it is very useful - passes trough the fuel filters! But I would still hesitate to mix it into solution of sugar and KNO3. But in case it would not self-incinerate during processing, it would give the second best result after the nanopowders.

I may post a fourth update to this article later.

Fourth update!

I dug up important information about many catalysts on a chinese university webpage.
It is a list of NOx decomposition catalysts sorted by their activity. This should serve as an additive aid to catalyst consideration, since CeO2 serves as a carbon "burninator" too. By combining some catalysts together we may get fast-burning solid substances that would hardly burn without the catalysts!

For rocket motor, I would like to try nano-powder of CeO2 plus some ordinary powder of Cu2O. The copper(IV) oxide might add instability and rapid pressure growth (lots of released oxygen), so my theory is to balance it with CeO2 so that it will burn the carbohydrate fuel evenly.

Nitrous Oxide Catalysts

List of reported N2O decomposition catalysts exceeds 200. [1-33]

According to Amphlett [3], the activity of metal oxides for nitrous oxide decomposition decreases in the following order:

CoO > CuO > NiO > MgO > Ce2O > CaO > BeO > Al2O3 > ZnO > TiO2, Fe2O3

According to Trapnell [4], the results of activity of metal oxides for nitrous oxide decomposition reported by three different groups in the following order:

CuO > MgO > Al2O3 > ZnO > CdO > TiO2 > Cr2O3 > Fe2O3 (by Schwab and co-wokers)

CoO > CuO > NiO > MgO > CeO2 > CaO > Al2O3 > ZnO > Fe2O3 (Schmid and Keller)

Cu2O > CuO > ZnO > Cr2O3 (by Dell, Stone and Tiley)

According to Clark [5], the activity of metal oxides for nitrous oxide decomposition decreases in the following order:

Cu2O > CoO > Mn2O3 > NiO > CuO > MgO > CaO > Ce2O > Al2O3 > ZnO > CdO > TiO2 > Cr2O3 > Fe2O3 > Ga2O3

According to Kapteijn the activity of zeolite catalysts decreases in the following order [6]:

Rh, Ru > Pd > Cu > Co > Fe > Pt > Ni > Mn


Plainly exciting, some scientists claim "The preparation and activity of copper zinc oxide catalysts for ambient temperature carbon monoxide oxidation". Carbon monoxide burning at room temperature. Well, we might add a bit of the zinc oxide to the catalyst too. (In car engines this is very important, in rocket science a bit less)

Labels: , , , , , , , ,