Transonic combustion 1

[black2003cobra]

Wondered what some of you folks thought about this. (Seems sort of like a combination of HCCI and DI...but different.)

http://www.technologyreview.com/energy/24701/?a=f

Test results seem impressive:

http://green.yahoo.com/blog/ecogeek...n-improves-gas-engine-efficiency-over-50.html

Maybe some of you have seen some other good references?

 

[JSteve2]

Just some general comments.

The primary benefit of CR it that it increases peak combustion temperature. Thus, the theoretical thermal efficiency is improved (see Carnot again). This is realized as improved useful work under the P-V diagram for the same amount of fuel.

It takes a large combustion temperature increase to move your thermal efficiency. For example, if your peak combustion temperature is 1500 F and exhaust is 800 F, your best possible efficiency is 36%. If you go up to 1800 F and keep exhaust at 800 F your best possible efficiency is 44%. To take it up to 70% would require 3730 F at the same exhaust temperature.

Cooling burden for increased CR should net lower, as more of the fuel energy went to work rather than heat. However, more of the heat goes into the block rather than out the exhaust because of higher heat transfer during combustion, so I'm not sure that would hold at all possible conditions. You lose more to friction due to higher cylinder pressures, but I don't know how significant that is.

Given the very low beneficial pressure remaining at the tail of the combustion, expansion ratio is a small fish (but non-zero). Look at a P-V diagram of a combustion event and think about how much beneficial area you could capture by delaying exhaust timing a bit - it's not going to be that much. Remember that a lot of those are logarithmic, so watch your scales or your eyes may lie to you.

 

[YvesLLewelyn]

JSteve2 - I think what you wrote is not quite right.
Higher CR may increase peak combustion temperature but this increase is from extra work done in compression - if the same amount of air and fuel is burnt the the increase in efficiency is due to the expansion ratio being greater (as other people have said).
The basic equation for thermal efficiency is - "one minus one over R to the point four". The "R" is the CR but it actually refers to the expansion ratio - the equation assumes that the compression and expansion ratios are the same. The actual compression ratio does not come into the equation.
On a P-V diagram the remaining temperature and pressure when the exhaust valve opens may appear to be very little - but remember that petrol engine exhaust manifolds are still hot enough to glow red - there is plenty of energy left when the exhaust valve opens. By raising the CR from 9:1 to 18:1 (for example), the extra expansion is enough to raise the TE by 10% or so - but there is little energy to be recovered after this point by further raising the CR/ER.
Speaking of glowing manifolds - I don't think a normally aspirated diesel manifold would ever get hot enough to glow - I've certainly never seen one glow.
A big part of the diesel's overall fuel efficiency is the reduction in intake pumping losses - possibly even slightly more that which comes from the increased ER.

 

[TStaples]

Black2003Cobra,

Due to our agreements with our partners, we are not disclosing the OEM's with which we are working. For obvious IP implications, employees are not allowed to share sensitive technical information. However, I will post links regarding public information as they come along. I can say that your dyno assumptions are correct.

I can only apologize to the engineering community for the marketing hyperbole. It's marketing's job to promote what we are doing, to a wide audience range. It's difficult to do that job without using descriptors like "revolutionary." YvesLLewelyn's comments reminded me that the reason that Engineers are not allowed to do marketing is that we are too literal. If an engineer were in charge at McDonalds, they would go bankrupt. No one would want to buy hot, dead cow.

JSteve2 is correct. Carnot tells us there is a lot of low hanging fruit in terms of IC engine efficiency. Because so little useful work is extracted from the fuel in terms of percentages, at low loads (like highway cruise,) it doesn't take a huge increase in overall efficiency to dramatically raise the fuel economy. Our website has a good explanation at:

http://www.tscombustion.com/autoinefficiency.html

I do have to take exception to Pat's broad brush statement that "pre-burning" fuel in a catalyst can only waste it. (I have a lot of respect for Pat, BTW, based on the depth of his contributions to Eng-Tips!) Theoretically speaking, lets assume you consume a small percentage of the energy content of the fuel in the catalyst, which then allows you to increase efficiency, via an otherwise unavailable mechanism, during combustion. If this mechanism saves more fuel than is consumed by the catalyst, at a given power level, then it results in a net gain. I wouldn't define that as a waste, when you look at the system as a whole.

-Tony Staples

http://www.tscombustion.com

 

[JSteve2]

Yves-
Carnot cares nothing about compression/expansion ratios. The "R" is the temperature. You need to know the temperature you are taking work from and the temperature of your heat sink to know the theoretical thermal efficiency. The fact that some of the temperature is from compression work is not relevant (but certainly not all of it - there are many reasons your peak combustion temperature goes up which go further than just the temperature increase by compression, see PatPrimmer's post for some of them).

Higher combustion temperature really is the driving force behind better efficiency with higher CRs. We could go crazy on this, but alas NOx emissions have come into play and we are trapped with 48-ish % thermal efficiency. I will call BS on any system claiming better than 48% thermal efficiency until I see the data and a good explanation.

Yes, there are a few percentage points to wring out at the end, but not very many, and it complicates other operations in the engine to try to get all of it. 10% is too big, but I won't hazard my own SWAG as it would likely be just as far off. I can tell you that if is was as high as 3%, someone would be doing it in certain applications already.

 

[black2003cobra]

Tony - Thanks again for stopping in. I appreciated the humor, by the way. The second SAE article you provided a link to earlier mentions CR in the range of 16-20, and 13 for gasoline engines. So was your test engine a CI or SI motor? Can you tell us what the brake fuel-conversion efficiency of the test motor is/was? Any other data you could provide would be appreciated.

Eric

 

[YvesLLewelyn]

Steve - the "R" I referred to in the equation "1 minus 1 over etc." is actually the compression/expansion ratio.
I realize I have confused matters slightly by using a capital "R" (which is normally the symbol for the Rankine temperature scale) - I should have used a small "r" - (starting to sound like a pirates' convention).
The quoted equation - "1 minus 1 over etc." is actually a different way of expressing the equation for thermal efficiency of "T1 (highest temperature) minus T2 (exhaust temperature) all over T1". T2 is the temperature that T1 is reduced to after adiabatic expansion by an "r" amount. I don't see that the amount of compression comes into the matter at all.
As for "applications" - the whole idea of the Atkinson Cycle is to wring a little more energy out of the tail of the P-V diagram - and the diesel as well is the same.
I would think that the TE of a 9:1 CR/18:1 ER Atkinson Cycle petrol engine operating at WOT/maximum torque RPM would have a very similar TE (if not a little better) to the TE of a comparable diesel - that is; something approaching 10% better than a normal 9:1 petrol engine.

 

[JSteve2]

Yves - I didn't look at the equation you were referring to, I just had thought you were indicating that the compression ratio was part of the Carnot equation. Atkinson certainly offers some assistance, I believe the Prius has a 38% TE. That's at least partially due to the fact that they can often run at a steady state point as well. However, since diesels regularly run 44% TE without Atkinson I think it's still clear that compression ratio is the bigger fish. I'm not saying there is no value in Atkinson in some circumstances, obviously the Prius gets some use out of it, but the numbers from the OP are not within my experience, and if they achieve them it's not primarily due to expansion ratio.

 

[TStaples]

Black2003cobra,

This page summarizes what we are publicly revealing about our technology. The term Diesel engine architecture is marketing speak for CI. I cannot discuss BSFC or other such data.

http://www.tscombustion.com/tscitechnology.html

-Tony Staples

http://www.tscombustion.com

 

[patprimmer]

I would have thought the method was proprietor, but the results would be shouted from the foof tops IF THEY WERE GOOD.

Everywhere I worked in technical marketing roles, a press release or technical data might go along the lines of:-

By improving the X process by Y we achieved an improvement in Z of Q% by test method M. The conditions were controlled by N

Further independent tests were carried out by the NATA registered laboratory B and their report can be supplied if you are interested. We can supply samples so you can conduct your own tests. Please contact us via XXXX for further action.

The proprietary details are of course not included. Hypothetically it might be something like we improve combustion efficiency and pressure build rate by controlling a:f mixture quality in a stratified zone within the chamber so that the nano particle size and localised control of a:f aids rapid but controled combustion.

Missing is the details of how you achieve and control the stratified charge and the fuel particle size.

I am starting to smell reptile oil here. The question is if it is very old or very new. My tip it is from a current living reptile like snake.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[msquared48]

For our dog Kennel, we tried to apply the Carnot Heat Cycle principles, but never with any success.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[TStaples]

Pat,

It's good for you to be skeptical. That is as it should be in Engineering. Fortunately, our OEM partners aren't consulting with you regarding your olfactory opinions! ;-)

As I've stated previously, I cannot share technical details that are not yet public due to legal obligations. It certainly isn't from a lack of personal desire. If I could, I WOULD be shouting from the rooftops. It has to do with the current stage of our company. IP protection is a very critical aspect of what we are doing, to protect the interest of our investors, stakeholders, and OEM partners.

I jumped in here merely to share the public information that I didn't see posted, per black2003cobra's original request. The kind of information you refer to is being shared with our OEM partners, after ensuring our IP is protected. This is not atypical in this type of situation.

-Tony Staples

http://www.tscombustion.com

 

[YvesLLewelyn]

Steve - In this Wiki article is an interesting list of various engines' TEs.

http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

The Prius Atkinson 13:1 ER engine is listed at 37% - other Otto engines are given as 27%. Both these figures would be with the engine running at its most efficient - so presumably the 13:1 Atkinson effect is worth about 10%. Note that 37% is a bit higher than the automotive diesels in the list which are up to 36%.
Presumably a Prius engine with an expansion ratio of 18:1 would have a TE of 40% or so - matching the TE of a normally aspirated 18:1 diesel - this is my argument - the TE is all in the ER.
Just how the Volvo truck engine listed makes nearly 45% is a bit of a mystery.
I have been interested for a long time in the reasons diesels have such a high TE - a lot of "high-powered" text books give the same reason as you - high CR and high combustion temperature - but I still think the major factor is the high ER - the high CR being a necessary evil.
I am quite happy to believe that there may be a valid thermodynamic reason why a diesel may have a slightly higher TE than an Atkinson engine of the same ER - but I don't know what it would be.


Atkinson engine of the same CR/ER

 

[JSteve2]

Yves,
You may notice that everything on that chart over 39% is direct injected, which enables high compression ratios. That Volvo truck engine is right in the mix for a modern on-highway truck - there are not many listed on that table but they are all in there (42-44 likely). If there were no other factors, that Prius Atkinson is worth about 37% (10/27), not merely 10%. However, there are a number of other factors, so it's difficult to say how much of that is attributable to the Atkinson portion alone.

For a heat engine, you only have two ways to improve the theoretical efficiency: increase the high temperature or decrease the low temperature. Extended expansion goes after the low end, and high compression goes after the high end. There is a limit to both - ambient air temperature at the bottom and your NOx generation limit at the top (unless you can ignore that - see the marine diesels at the bottom of that chart). Also, high ER in the absence of high CR yields a very low power density. The Prius survives that because it is a hybrid (98 hp out of 1.8 L).

Of course, there are any number of ways to go after actually achieving your theoretical efficiency once you establish it, but you can never go over it.

We could just be having a debate on terms. A high ER by it's nature indicates a high difference between the combustion temperature and the exhaust temperature - think about the cylinder conditions after the combustion chamber has expanded 18:1. Whether you achieve a high ER by starting with a high CR or by delaying exhaust opening, it may not matter too much how one thinks about it.

There may be more to a profound ER than my instincts were telling me initially. It will be interesting if someone develops a commercial high ER product that explores the limits of that.

 

[SomptingGuy]

I'm just looking forward to seeing the demonstrator vehicle when it hits the streets. Can one of you TS employees be sure to start a new thread when the vehicle is available.

- Steve

 

[patprimmer]

On studying the data and papers as presented, I find the figures hard to justify as there are no fixed points of reference. 50% better than what. A T model Ford ?

Also while some of the techniques mentioned are not exactly new, there is reason to expect they may improve fuel economy if other traditional problems are solved, however the magnitude claimed is frankly unbelievable.

As you are a consultant I can appreciate that you should be ultra conservative about releasing anything about a customers project.

One of the papers I had not previously read does give the mechanisms but not the details with regard to rapid combustion and stratified charge and fuel regulated rather than throttle regulated diesel like features.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[TStaples]

black2003cobra,

Here are a couple of additional links that are fairly good public overviews of what Transonic is doing. The second includes a link to a video of Transonic's VP of Marketing giving a reporter an overview during the ARPA-E summit.

http://www.peswiki.com/index.php/Directory:Transonic_Combusion_--_TSCi_Technology

http://www.trendhunter.com/trends/super-efficient-fuel-injection

-Tony Staples

http://www.tscombustion.com

 

[black2003cobra]

Well not really knowing what cycle to use, just for the heck of it, I ran a quick thermodynamic simulation for two cases just for the standard Otto cycle. I just used “ideal” (non-realistic) valve timing.

For the first case, I used rc = 9.5, a burn duration of 50 degrees, spark at MBTT, and an equiv ratio = 1.

Then for the second case, I used rc = 20, a burn duration of 20 degrees, spark at MBTT, but backed off on the equiv ratio until indicated work from both motors were the same.

I found that therm-conv efficiency went up by about 22%, and comb efficiency by about 2.5%. The combustion efficiency was taken from a fit to a data plot, and it’s a little shaky, at best. I recall other plots in Heywood for fuel-conv eff vs equiv ratio, and I should take a look at that. It would be more accurate. Be that as it may, from just a crude estimate here, the model results are suggesting around 25% improvement. Most from just the higher rc.

Because I used less fuel to get the same gross work, peak temps weren’t much different. Peak pressure was significantly higher for the high-rc/short-burn case, however. The heat transfer was definitely higher around peak pressure for the high-rc/short-burn case, but then dropped below that of the lower-rc/long-burn case throughout most of the expansion stroke. Overall, there was less heat transfer through the cylinder walls and out the exhaust for the high-rc/short-burn case.

(The model uses Woschni’s hc for convective heat-xfer and a black-body approximation for radiative heat losses. The later, being fairly small by comparison. Burn is via Wiebe burn fraction. It does not include frictional losses, nor did I include pmep losses.)

So some additional improvement should certainly be possible by eliminating pumping losses from the throttle. Not sure how much that might improve overall mech efficiency, but someone might take a wag at it. I am not confident it would get the overall fuel-conv efficiency up enough to show a 50% improvement. But again…maybe someone has some numbers to throw at that.

I am a bit confused by what the reported gain in fuel-conv efficiency really is. The SAE 7160 article (link given by Tony above) says it doubled. This other article (link below) says a 50% increase. It says,

“That’s where a new system from Transonic Combustion comes in. The California-based startup has developed a fuel-injection system that can improve the efficiency of gasoline engines by 50%.”

Here is the link =>

http://www.inhabitat.com/2010/03/09/transonic-combustions-super-efficient-gas-engine-gets-98-mpg/

The other peswiki.com link in Tony's post above suggests 50-75%. It would be good to know what the true baseline is.

Thanks for the other links, Tony.

Regards,
Eric

 

[black2003cobra]

Just noticed in the peswiki.com link that it mentions a modified gasoline engine was used. I interpret that to mean an SI engine. But no spark for transonic setup, I assume. Mentions a doubling of ?f,b.

"Test Results
Company engineers have doubled the fuel efficiency numbers in dynamometer tests of gas engines fitted with the company’s prototype SC fuel-injection systems. A modified gasoline engine installed in a 3200-lb (1451-kg) test vehicle, for example, is getting the equivalent of 98 mpg (41.6 km/L) when running at a steady 50 mph (80 km/h) in the lab. The new technology is achieving significant reductions in engine-out emissions. Some test engines reportedly generate only 55-58 g/km of CO2, a figure that is less than half the fleet average value established by the European Union for 2012."

 

[TStaples]

black2003cobra,

I didn't notice that error in the peswiki article. It was a modified compression ignition engine. That was an error by the author. That has been published correctly in other articles. Good catch. I try to only post articles that are reasonably accurate. (We recently got written up by our local newspaper, and the article was flattering, but so full of technical errors, that I see no sense in sharing. Non-technical people have a hard time writing about technical things.)

-Tony Staples

http://www.tscombustion.com

 

[black2003cobra]

Looks like the SAE 7160 article is wrong, too. (Looks like a direct copy to me.) Thanks for the clarification, Tony.

Eric