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"Variation of engine combustion efficiency with fuel/air equivalence ratio, on Page 82 of Heywood's Internal combustion engine fundamentals. The 80% corresponds to equivalence ratio of 1.1. As the ratio gets to close to 1.0, the efficiency is close to 90%. And the case for diesel is 95-98% at 0.8 equivalence ratio."
I don't have Heywood to hand but I'm pretty sure you are misinterpreting that. I'll be back at my desk on Monday and will check it then.
I have been getting feedback from my friend regarding the effect of friction.
Let us get the context correct. It is a 6 stroke engine. The design goal is NOT a normal car engine but a gasoline engine that runs at full load and low speed. Air pollution goal is 100% coverage, and efficiency goal well over 40% thermal efficiency. The application is ideally a small airplane engine and of course hybrid car.
The data I shall quote is from the same book by Heywood. On page 797. fig. 14-28. Titled distribution of available energy into major categories. Although it is for turbo diesel engine, but the friction and flow loss is the same for spark ignition engine. We want the friction loss as small as possible, so we run the engine at 1000 rpm, full load. The friction loss(including flow ) is 3% of available fuel energy for 4 stroke engine. For 6 stroke engine the loss will be 50% greater and we have 4.5% loss a 1.5% increase. In the discussion previously, we have fully vaporized, lean and uniform mixture and with stratified charge ignition, the combustion efficiency improvement is 10% conservatively. The improvement in brake energy is about 40 x 0.1 = 4%. Now our mechanical energy gain must subtract our additional friction loss of 1.5%, and finally we have net 2.5% gain of the original 40%. Finally our thermal efficiency is 42.5%
This may seem unreasonable. Trust me. It is. The trick of this gain is low rpm and full load, as I stated at the very beginning. I hope this explanation will satisfy those with severe doubts.
The world's most efficient internal combustion engine is a marine turbo diesel achieving 170g/kw-hr, or 50% thermal efficiency. It does not have camshaft (individual activated valves) and use special lubricants. This is the theoretical
limit of thermal efficiency for any ICE.
Aren't those huge/thermally efficient C.I. marine engines - in fact operating on the 2-stroke principle?
How will going 6-stroke actually improve on these,(with all the extra non-productive pumping/reciprocation)?
"Well, we knocked the bastard off!"
Ed Hilary on being 1st to top Mt Everest,
(& 1st to do a surface traverse across Antarctica,
in good Kiwi style - riding a Massey Ferguson farm
tractor - with a few extemporised mod's to hack the task).
@ Chen
how does the engine (large relative to its power at 1000 rpm) compare in efficiency with a smaller engine run at higher rpm ?
for a given power won't the smaller engine have smaller heat loss to coolant and no greater friction ?
Absolutely It is a two stroke diesel. I think it is turbo charged to get maximum efficiency.
The point I want to make is for maximum efficiency, especially for a diesel for marine use, it must be operated at low or very low speed and full load.
Yes, two stroke helps, as it halves the friction and flow loss. And they do not have to worry about EPA.
Regarding my misunderstanding of combustion efficiency, I re-read the Heywood's book. He defined thermal efficiency as fuel efficiency and it is the product of combustion efficiency and what he called thermal conversion efficiency.
When applied to our case, the individual pressure pulses by the ignition/combustion and their phases with repspect to crank angle is the thermal conversion efficiency. If you have all the combustion efficiency but the timing is wrong, you still have no work done.
Yes, I misunderstood stratified charge. But, for very lean mixture, isn't stratified charge ignition a must???? A final ignition fuel injection spray is given.
For Cookers, the data I have all indicate that friction loss increases (as percentage) monotonically with rpm.
Mr. Chen (if that is correct) , may i ask if your design has the two extra strokes to homogenise the mixture better for improved combustion?
How do you see the lower power density (in relation to time) ? is that solved through multiple cylinders?
As I stated before, in fact first post, the shortcoming of this 6 stroke engine is lower power, as you would say lower power density. Again you are correct, it can be "corrected" (if that is the word) by more cylinders, or just more displacement. Turbo would not help much, as I need to run at very low RPM.
In summary, this 6 stroke engine is a LOW ENERGY ENGINE. The feature is efficiency and cleanliness. For more efficiency and power(10% roughly), you need first part of Chen engine "exhaust purge" at low RPM and full load.
As I thought your interpretation of Heywood is ludicrous cherry picking.
Here's what he writes about SI engines "for lean equivalence ratios the CE is in the range 95 to 98%"
Sure, if you pick a point on that graph where the engine is running rich, there is a lower combustion efficiency. But you don't operate your engine with excess fuel if you are going for fuel economy, you use fuel enrichment for cold satrt and for valve/cat cooling at high power. Here's a random example, note that the base AF ratio is stoich for most typical driving conditions.
Yes, I pick the data that support my thesis. Within reason, that is allowed, right. Still, the engine should run slightly rich for not only the reason you mentioned but for safety margin, engine out of tune etc. This is the operating point for airplane engines. They need larger safety margin. Nonetheless, I accept your objection.
The second part of the efficiency has to do with converting heat energy to mechanical work. This is the consistent pressure pulses at exactly the right time, a 6 stroke engine will provide. You have Heywood's book and he provided many pressure traces and his conclusion of shot to shot variation. Again, this must have been a well prepared engine at best operating point, so he would not be biased. But in the real world, it is worse, as spark timing out of tune etc.
You talked about cold starting. I am speculating that 6 stroke engine may not have this problem. The piston will compression heat the fuel much more than 4 stroke engine, especially with direct injection. At this point I just speculate. OK. I do not know. Maybe direct injected 4 stroke engine solved this problem already with just its compression heating.
At this point I would like to thank you again for your criticisms and support, especially from last time. I should not be making untrue statements.
Greg, I went back to the graph of combustion efficiency of Heywood. There is no reference to this graph.
Even though Heywood said gasoline combustion efficiency is "usually" in the range of 95-98, but the graph data are truly too scattered. He did not even bother(able) to make a LMS curve fit. They are too scattered to get a fit.
For reader who does have access to this graph, I must point out that one datum shows 88% efficiency at 0.9 equivalence ratio and another one 91% at 0.65. We do not know how the data is collected or processed. One thing is certain, Gasoline combustion is far (about 4) more erratic than diesel combustion as indicated by the scatter of data. That fact points directly to chaotic state of charge during combustion. This point is important for the merit of 6 stroke engine.
I understand your objection, but this point is too important to give in.
You are cherry picking.I hope your potential investors are reading this thread. Look at the actual air fuel ratio used by modern SI engines when they are operating normally. Big clue, if they've got wideband O2 sensors they'll be operating in a very narrow range of AF ratio.
Let us say that at 1.0 equivalence ratio the data showed 90-98 % range. I am getting another 10% improvement with all the pressure pulses hitting the sweet spot for maximum thermal to mechanical conversion. (In other word, maximum torque spark advance). Since I operate at only a single operating point, load, and rpm, this point is fixed and need not be mapped through out the regular auto engine working range.
I would sincerely like to remind you that the idea of entire project(Chen engine) is to avoid using three-way catalytic converter entirely. Please no Oxygen sensors. For 6 stroke engine the window of acceptable fuel air mixture will be very large, from 0.7 to 0.8, with stratified fuel rich ignition of course.
I do not expect any investment on this 6 stroke engine, as the development to commercialization will run up to billion.
But I am optimistic that in face of increasing electric car competition and hybrid cars, the big guys in automobile will invest in this "ultimate" combustion engine for use in future hybrid cars. For established engine manufacturers, the development will be only very small fraction of the full initial funding to commercialization. I estimate only 10 million will be enough for prototypes, with six stroke and exhaust flush. A total of three prototypes, Two separate ones then a combined prototype.
Chen engine needs two parts to achieve best efficiency and lowest pollution. This thread covers 6 stroke engine.
I would like to write down a few thoughts on "exhaust purging". Ideally there will be a short pressure air injection at final phase of exhaust cycle at TDC. The actuating valve is not mature enough for use(Koenigsegg). The second best choice is turbo charging with only <0.5 ATM, just enough to flush exhaust.
The consequences are , the charge will be thicker and uniformity will be worse than for normal charge. On the other hand, the power density will be greater and for the same displacement engine, the power will be greater. It is an engineering trade off. Efficiency vs Power.
On the other hand, turbo works only above 1500 rpm, even for fastest acting turbo. There is a need to develop lower engine speed turbo. Since 6 stoke engine runs always at full load, the volume of exhaust gas may activate the turbo.
The air requirement is only the same as 4 stroke engine,even less by 1/3. It will not tax turbo. And of course the exhaust has 1/3 less volume than 4 stroke engine.
In any case, "exhaust purging" is a must for Chen engine.
I read, that Porsche can not pass pollution test with their famous N/A engines. They have to install turbo engines on all except one, of their new sports cars. Thanks to "exhaust purge" by turbocharging
& to paraphrase Sir Stanley Hooker, '6 strokes provide one power-stroke, plus 5 - to wear the engine out'.
Perhaps Mr Chen could join forces with fellow member here, & also self-proclaimed 'prophet'
- of advanced spoonbending, ah, sorry, - I mean 'advanced engines' -'Feliks', & amaze us all, yet!
This practice of ad hominem is not constructive.
mr chen is simply exploring engineering paths, so a discussion of the pros and cons is best.
"Ad hominem"?
I dont think so Johnny C-L, & my paraphrasing of Hooker's view - is surely apropos on a 'technical' basis.
& I'll add a Christopher Hitchens dictum here:
'What is asserted sans evidence, may be dismissed, accordingly'.
If Mr Chen can prove his ideas do not belong in the 'crackpot' category - ( via 'the pudding') ok, fine,
but frankly, if you review his prior claims - as posted on this forum - the probability aint high, IMO..
Well they should have just used Reitz RCCI in conventional diesel engine that's already achieved 59.3% thermal efficiency with lots of optimisation left to go, with only minor piston redesign more like gasoline piston and turning off the piston oil cooler. So 4 strokes gives the best combustion and thermal efficiency.
Mechanical efficiency is really high now, the gains really are in combustion and thermal. Losses to friction so small in well designed engine just not much to be gained anymore.
that seems to be 59.3% gross indicated thermal efficiency
and so quite a distance from 59.3% overall efficiency
sadly many here and in Mercedes PR wrongly think thermal efficiency is another name for a heat engine's overall efficiency
they don't accept the historically established concept whereby different names connote different things
