Diesel fuel possibilities 3

[FahlinRacing]

I have been on the hunt for a buddy who runs truck pulls and was curious on what I could do to improve the burn cycle by engineering a performance fuel. I had seen Mr Primmer mentioning Acetone does help, however I believe it kind of dries out the Diesel fuel since it is a solvent. In turn needing a lube additive no matter what. I had the idea of Biod for its lube properties and high Cetane quality.

The ideas I have had so far are using BioD, methanol, ethonal or another that could be mixed in. But, some are saying I will need some equipment to mix it properly and efficiently on whatever I decide on. I believe methanol can only be injected, assuming ethanol is the same way? Along with other additives, I would like to use another actual fuel if I can.

Any insight would be greatly appreciated!

 

[mattsooty]

Fair one Pat, and I hope you didn't think I was being patronising.
My understanding is that, as a combustion system, heterogeneous charge compression ignition engines are still very much pigeon holded & are yet to break into the performance game proper - hence a lack of literature.
Ms

 

[FahlinRacing]

Mechanic6, that is another reason I am trying to improve the fuel. USLD needs more lubricity not only to reduce fuel shearing caused on the passage surfaces during the oil's travels to the injector but the injection itself. Viscosity has influence on the injection quality along with lubrication. Thank you for bringing it, GTL, up. I will check it out when I can.

Matt & pat if I had a used up engine I could test and not worry about melting things, I would be already running mixtures of this or that and see what happens. Any other thoughts, I appreciate this insightful discussion guys!

 

[patprimmer]

Matt

No problem. I certainly did not take it as patronising. Many SI engine guys know little of CI, myself included and I know that I don't know and I am always eager to learn.

Your posts are some of those I really look out for as they often contains gems I was unaware of.

Regards
Pat
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[SMOKEY44211]

I think fogging in hydrogen will get you what you are after.-------Phil

 

[rmw]

But what happened to diesels back in the day that fumigating with Propane was all the rage? Won't the same thing happen with the OP's engine if he finds something to blend or fog or fumigate?

rmw

 

[ivymike]

Not if he fumigates with hydrogen, I expect a much more abrupt end in that case.

 

[Lou Scannon]

Pure methanol can indeed produce more power in a compression ignition engine than typical diesel fuel, if the engine is optimised for it. But a means of initiating combustion is needed, either a glow plug, or an additive such as Avocet. And of course the entire fuel system needs to be engineered to handle methanol, both due the increased volumetric flow, as well as the lack of lubricity and corrosiveness.
I think the development effort of engineering a 1-off methanol engine for tractor pulls is not justified by the return in performance, compared to the traditional methods of more boost, more fuel, & beefing up the mechanicals as needed.
Assuming fuel rate is not a limitation, the goal is to get the highest oxygen density in the charge as possible and match it with fuel, up to the engine's mechanical limit. Other than boost, you can increase the oxygen density by fogging with nitrous oxide, or even pure oxygen. I would caution against pure oxygen though; too many hazard and I doubt it would be allowed at the race course anyway.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[140Airpower]

hemi, Nitrous Oxide is an excellent source of additional oxygen. It is also an anti-detonant, resisting autoignition, and might also require that a glow plug be used. Is there a disadvantage in using glow plugs?

 

[Lou Scannon]

I don't know that N2O is an anti-detonant per se, it is just a source of oxygen enrichment. When it is added in liquid phase to the charge, there is a substantial benefit from the heat of evaporation in cooling the charge. The cooling effect of course improves charge density, and offsets thermal loading of the engine; and in Otto cycle engines, the net cooling can provide margin against knock/detonation.
At any rate, compression ignition engines do not have a detonation issue, under any normal conditions.
There is no particular technical disadvantage with using a glow plug (i.e. to assist ignition in a compression ignition engine), but if the engine is not designed for glow plugs, they will be difficult to add after the fact. Glow plugs are designed for intermittent use only (starting, idle, & low load). Even with methanol they are not necessarily required 100% of the time, but the required glow plug duty cycle with methanol will be high compared to diesel (especially direct injection engines, which have no glow plug, so the diesel duty cycle is 0%). Using glow plugs at higher than the intended duty cycle will accelerate their demise.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[140Airpower]

hemi, that clears up some questions about glow plugs. One factor with Nitrous as a power booster is that it would be used under high power conditions, so I suppose the need for a glow plug would be minimal or more likely not at all. It is an anti-detonant in SI engines according to Ricardo, which is a great benefit under the conditions in which it is used in SI engines. He compared it to liquid Oxygen which they found to be a pro-detonant. But, I don't think you can assign an ON for Nitrous.

 

[BigClive]

Like a few other people here I have to confess to not knowing a lot about diesels.
However as I understand it the problem with lack of power etc. from a diesel is its slow rate of fuel burn and consequently the engine's lack of ability to use up all the available oxygen. This is apparently mainly due to the particle size of the injected fuel droplets.
Why not inject the fuel at a very high temperature? Not high enough to cause coking problems but hot enough so that the the injected fuel immediately flashes into a vapour form (not droplet form at all) and the high temp also would increase the burning rate.
I realize that there would be a few technical problems - the fuel could only be heated just before it enters the cylinder, the injectors would need to be able to operate at a very high temp etc. - but the problems would not appear to be particularly insurmountable. Has it ever been tried?

You could even extend the idea to the direct injection of petrol into a typical SI engine with a CR of 10:1 or so - without the spark ignition operating and the fuel igniting because of its high temp. as it enters the cylinder - load control being by the amount of petrol injected, the engine operating at WOT.

 

[FahlinRacing]

The work stock or 2.6 4x4s fuel is only allowed No1 or No2 or Bio with additives albeit no 'oxygen extenders', fumigation systems aren't aloowed or other injection systems either. But, I haven't looked at other classes to see what fuel system and fuels are allowed with Super farm or Prostockers. Very interesting conversation here and I am taking notes from you helpful folks!! If I can't seen to get much for a work stock fuel mixture to improve combustion, atleast I have been provided some great ideas and insight here. I'll have to grab some snack and catch up here, I have been busy building onto my deck outside.

I watched one of the top Prostock tractors in the country last night, boy does that engine sing when its at WOT.

BigClive, good thought on heating the fuel to promote vaporization, but, then if we raise the fuel temp above normal engine operation temp we should take into account how the wear of the injector and other components would be effected in result of raising the temperature.

Another thing we will have to look at would be our piston crown surface finish to help keep our fuel off and from puddling if impingement is a problem.

 

[Lou Scannon]

BigClive, there are definite advantages to injecting droplets rather than vapour. In order for the injected fuel to get exposure to the available oxygen in the combustion chamber, it needs to penetrate far enough to do access the oxygen at the extremities of the chamber. Droplets will penetrate further than a vapour plume, for a given injection pressure.
State of the art common rail systems are now operating in the 30,000 psi range. I have no idea how much higher would be needed to get the same penetration with vapour, but I suspect it would be a pretty tall order to develop a pump and injectors to do this.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[Tekton]

This doesn't sound correct

IDI engine technology requires a pre combustion chamber to ensure the atomised fuel vapourises and initiates combustion within the comparitively oxygen rare confines of the chamber before emerging through the pre combustion chamber port, ricocheting off the specially shaped piston crown, mingling with chaotically swirling/tumbling air, and combusting with the oxygen present

Modern direct injection diesels employ high injection pressures & electronically controlled injectors, whose low mass components and nozzles with multiple, comparitively minute orifices ensure fuel is atomised into ever finer droplets, whilst delivering as many as 5 distinctly separate "puffs" of fuel per combustion cycle

The purpose of multiple injections is to create a minute space within the combustion chamber where fuel and oxygen may combust, into which the next batch of atomised fuel is delivered

The freshly injected atomised fuel introduced into that high temperature, oxygen depleted environment has sufficient time to completely vapourise before mingling and combusting with oxygen in the "fresh" air it soon encounters, thus simulating the dynamic of a pre combustion chamber - - without its disadvantages

Regardless of pressure, calibration, phasing, and droplet size, continuously injected diesel fuel lacks the opportunity to vapourise, homogenise, and combust as effectively as IDI and multiple injection DI systems

For proof, look at the trends exhibited by manufacturers whose contemporary diesels are employed in everything from passenger vehicles to road transport and industry

Tekton

 

[BigClive]

Hemi - I think I am agreeing with Tekton (sounds like an alien) here - I would have thought that as well as a "plume" of vapour reaching all the available oxygen, turbulence in the combustion chamber would tend to also bring the oxygen to the fuel - in fact, turbulence would tend to thoroughly mix the fuel vapour and oxygen.
If what you say is correct, wouldn't GDI SI engines have the same problem?

 

[Tekton]

This report provides dramatic proof of how severely engine performance and emissions are affected when the uninformed and/or ignorant alter an IDI engine's oe specifications

Indirect Diesel Injection engines, though rapidly being superseded by the direct injection designs permitted by superior materials, machining, and electronics technology, are non the less still specified for many industrial power plants where low noise levels and durability - - when in oe form - - are desired

However, Worldwide millions of crudely maintained and modified IDI engines are dying a premature death whilst hastening ours due to the excessive exhaust emissions they produce when carelessly - - or deliberately - - maintained or modified

Tekton

 

[Lou Scannon]

I'll grant that Tekton's knowledge of diesel injection combustion is obviously more informed and current than mine. So thanks for the input. I was trying to find the right words when I originally composed my post. My intended meaning is better served by changing "chamber" to "combustion space"; I know that combustion doesn't extend to the physical limits of the chamber by any means, but the proper wording failed me at the time.

So, question for Tekton: what is a typical penetration distance required by current technology common rail diesel injection (maybe as % of bore diameter)?

The problems with GDI injection are not the same (and probably not as difficult, with respect to injector & pump design, since the desired results can be achieved with a fraction of the rail pressure compared to common rail diesel). Typically the goal with GDI is to have the charge preparation complete (or nearly so) at the beginning of ignition. That means mixing all of the fuel with enough oxygen to ensure complete combustion. Note that this applies to both homogeneous and stratified charge combustion. That said, penetration distance is a key parameter with GDI injection and is one that a lot of effort goes into ensuring suitable penetration under the obviously very wide range of speed/load operating conditions.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[Tekton]

Hemi, I wish I could expound, as the finer points of combustion technology have fascinated me for decades

I became acquainted with IDI components and combustion technology during general study a generation ago, then intimately in the late 90's when developing a range of pre combustion cups and belatedly recognising no comparative information was available for parts stockists and service personnel

This attachment is one of many intended to educate the above and expose the rampant use of incorrectly dimensioned parts such as those responsible for the Mitsubishi exhaust emissions

A complementary series of component dimensional listings etc was also developed

"Engine Technology International" keeps me informed of current trends

Fahlin Racing, my apologies if I've sidetracked the thread

Tekton

 

[mattsooty]

Just a quick refresh of the main fundamental difference between a gasoline SI engine and a diesel CI engine which is, quite obviously, the combustion process.

Within an SI engine, operating under normal conditions, the sequence is: -
Mixture Formation - Combustion Initiation - Kernel Formation - Rapid Combustion - Exhaust

A homogenous charge is formed within the cylinder volume, either through fuel being introduced into the air charge, remotely from the cylinder, or injected directly within the cylinder.
Upon firing the spark plug, a laminar flame spreads from the spark plug electrodes and a roughly spherical flame kernel is formed. This then quickly develops into a turbulent flame, due to in-cylinder gas motion; with this motion increasing the burn rate of the charge. All before the end gases auto ignite and cause Detonation.

Within a Common Rail Direct Injection CI engine, again under normal operating conditions, the sequence is: -
Start Of Injection - Ignition Delay - Premixed Combustion - Mixing Controlled Combustion & EOI - Late Combustion - Exhaust

After the start of injection, directly within the cylinder, a heterogeneous charge is formed by way of a jet of high pressure fuel at the edges of which liquid fuel sits in suspension as droplets, slowly evaporating within the relatively low in-cylinder temps.
Around these droplets sit local pockets of vapour, some of which possess an AFR within the combustible range. As the compression stroke continues the temperature within the cylinder increases and these combustible areas begin to do so, spontaneously. This Premixed Combustion can and does occur simultaneously in many different areas at once and is, in some ways, analogous to detonation in an SI engine, with a rapid rate of pressure change. This is associated with the characteristic Diesel Knock/Combustion Noise & damage to engine internals.

The Premixed Phase develops into the Mixing Controlled Phase; as the fuel continues to be injected the pressures, temps, charge kinetic energy & rates of evaporation all increase. The rate at which the fuel is burnt relies upon the fuel molecules being exposed to O2 in the correct ratio with which to react and the formation of areas of combustible AFR mixture. This is a function of the available O2 (boost pressure & internal EGR) and in-cylinder charge behaviour i.e. rate of evaporation/fuel quality.

So, for a given CI engine & fuel type, to increase the torque produced the mass of fuel injected is the dominant factor and is a function of (Rail Pressure, Injection Duration).
The Injection Duration (SOI to EOI) is always constrained by the following: -
SOI
The piston must be near enough to TDC to allow the injected fuel to be within the bowl of the piston and not impinge on the relatively cold walls of the cylinder – or some of the fuel is wasted.
With this as the maximum, the advance of the position of SOI towards such is also further restricted by an increase in Ignition Delay. This is due to charge temps being too low to promote vaporisation, and therefore combustion, leaving the fuel ‘sitting around’ waiting to be combusted. Which, when it does, tends to occur in one bulk reaction.

EOI
For good mixing & therefore combustion to occur, the EOI must occur before the injection spray misses the piston bowl where gas velocities begin to slow drastically (bearing in mind reduced O2 & increased EGR). Good combustion therefore begins to rapidly diminish, as the piston moves towards BDC. Another constrain on EOI is the increase of exhaust temps due to slow reacting fuel.

Once the above constraints are encountered the only way to achieve more torque is to inject the fuel at a higher pressure with a corresponding increase in boost pressure (available O2 & compression).
More boost pressure means more available O2 and higher compression temps with a decrease of Ignition Delay but an increase in rate of overall pressure rise, a higher peak pressure and a shorter combustion duration – certain provision can be made to offset this by intercooling the boosted charge. Exhaust temps are also reduced (analogous to advancing the spark in an SI engine) as the burn duration is reduced. However, the increase in rate of pressure rise can be, as mentioned above, very damaging to engine internals in the same way that knocking in an SI engine can be.

So, in a nutshell, the challenge is to be able to inject enough fuel between the piston position constraints of SOI & EOI without an excessive Ignition Delay and provide an acceptable rate of pressure increase during Premixed Combustion. Whilst moderating the rate of pressure rise and decreased burn duration during Mixing Controlled Combustion but reducing the high exhaust temps that occur (the Late Combustion) due to the excessive fuelling by increasing boost pressure/reducing charge temps.
And that’s before we start talking about smoke…..

See why I hate Diesels?

MS

ps please attribute any typos etc to the few G&Ts I've imbibed, just to wet the whistle!

 

[Lou Scannon]

MS, that was a nice synopsis. We both know there are many nuances beyond the scope of your summary, but it's somewhat of an oxymoron for a summary to be comprehensive. A star to you!

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz