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Diesel-Like Engine Could Boost Fuel Economy By 50%
bonch writes "Autoparts manufacturer Delphi has developed a diesel-like ignition engine running on gasoline, providing a potential 50 percent efficiency improvement over existing gas-powered engines. Engineers have long sought to run diesel-like engines on gasoline for its higher efficiency and low emissions. Delphi's engine, using a technique called gasoline-direct-injection compression ignition, could rival the performance of hybrid automobiles at a cheaper cost."
FTFA: Diesel is dirty and requires expensive exhaust systems.
The key distinction, as I'm aware, between diesel and gasoline is all about the ignition to begin with. In a gas engine, you create a spark to ignite a carefully mixed gas/air vapor. In a diesel, you don't need the spark, instead using sheer pressure from a much higher compression ratio. (this also leads to higher power per stroke, and therefore greater theoretical efficiency) Presumably they've found some way to reliably ignite gasoline without said spark, thus reaping the same compression ratio benefits or some such thing, I would guess.
What keeps diesel engines from becoming a standard in the US? I know regulations nearly disappeared them from the market, but that was for environmental reasons, which are the very reasons why diesel cars are attractive. While in Europe it is not outside the norm, here it seems like you are committing a crime if you run a diesel engine.
Also - since diesel engines are so efficient and all - what stops them from making a hybrid car that benefits from the even greater efficiency of diesel? or this new type of diesel like gas engine for that matter?
Many reasons diesel hasn't been popular in the U.S. One reason is environmental concerns - at least in the north east U.S. and California, our emissions standards, particularly for particulates and sulfur compounds, are much stricter than Europe. A second reason is that people tend to buy cars based on horsepower, and diesels lag there. Third, lots of people have bad memories of noisy, smelly diesel engines from the 80's. Fourth, diesels cost more. All that said, they are making a comeback with the newer offerings from VW and BMW (and Mercedes?).
I believe the reason diesels haven't been seen in hybrids is a combination of several factors. One, they are heavier than gasoline engines which in a hybrid already facing weight issues due to batteries could be a problem. Second, they are more expensive than gasoline engines, and again hybrids already face a cost problem. Third, the efficiency gains using gasoline engines have been sufficient to set them significantly apart from most non-hybrid cars, so the additional mileage you might get from using a diesel instead isn't worth the additional cost and weight.
It is niether a bad idea nor magic. By pulsing injections they make the combustion behave closer to the Carnot cycle ideal, which is more efficient than the Otto cycle.
That aside, I have my doubts about the 50% improvement. And diesels are already closer to the Carnot cycle so you could say they are effectively running a diesel on gasoline.
One important benefit it could have over diesels though, is that diesel burns fairly slowly compared to gasoline - which is the reason why diesels rarely rev above 5000 or so. If they manage to get diesel-type efficiency but with faster-burning gasoline, it could result in an engine that feels and behaves like a gasoline engine but has the mileage of a diesel. That would be nice.
It's probably inevitable-- it's just a question of when. Battery cost per kWh has been decreasing at around 10% per year, and gasoline is getting consistently more expensive. It seems incredibly unlikely that both of these would stop moving toward the crossover point.
Gasoline engines have been keeping up with that 10% though. In 1998 the Ford Mustang GT with a 4.6L V8 had about 215hp. In 2011 the Mustang GT 5.0L V8 packed in 412hp. That's about 7% a year increase in power and a slight increase in mileage. It stands to reason if that extra efficiency was put towards more mpg instead of more power, that crossover point could be farther out than you think.
The good news is it's getting better on both fronts and fast!
I have my doubts about the 50% improvement.
Careful reading reveals that your doubt is well placed, but you misread their claim:
technology that could improve the fuel economy of gas-powered cars by 50 percent...Diesel engines are 40 to 45 percent efficient in using the energy in fuel to propel a vehicle, compared to roughly 30 percent efficiency for gasoline engines.
So all they really claim is that a diesel engine that runs on gasoline has roughly the same efficiency as a fuel-oil powered diesel.
It means "I approve of the above message which neatly encapsulates most of my feelings on the matter".
If you work out the math of various combustion-work cycles (see Otto Cycle, Diesel Cycle), and then take a look at how they are implemented in a typical gasoline or diesel engine, one of the things you immediately find is that efficiency is directly proportional to compression ratio. That is, the more you compress the air (or air-fuel mixture) before igniting the fuel, the better your efficiency.
Gasoline engines tend to be limited in their compression ratios, because if you compress the air-fuel mixture too much, it'll spontaneously ignite while the piston is on the upstroke, a phenomenon called pre-ignition or engine knock (because of how it sounds, I suppose). Diesel fuel burns a bit differently than gasoline, and diesel engines take advantage of spontaneous ignition: they purposefully have high compression ratios to heat up air in the cylinder, then inject the fuel when the piston is at/near the top of its stroke, where it immediately ignites. But diesel, as a fuel, has some practical downsides which has limited its more widespread adoption, primarily how cleanly it burns.
If, on the other hand, you could produce an gasoline engine that uses diesel-like compression ratios, and inject the gasoline at maximum compression, as a diesel engine does, you could have the best of both world: greater efficiency due to high compression ratio, cleaner running due to burning gasoline. But such an engine, for various technical reasons, has historically been difficult to achieve. Maybe these guys are really on to something.
Well, as the article pointed out, they are using a much finer grained control of the injection precisely to control knock, injecting fuel in up to three shorter bursts.
This also allows them to space those bursts at precise times during the power stroke, such as when the piston is going down, and the expansion of the initial burst of fuel is losing effectiveness due to combustion chamber expansion reducing the instantaneous pressure. Adding a burst of fuel at that point gets you extra power at what would otherwise be the downward (backside) of the power curve.
Previous approaches to this were attempted with variable valve actuation, (essentially getting rid of the cam shaft and using other means of controlling valves more precisely). Costly, but effective.
This approach (precisely controlling fuel delivery) allows you to shape the combustion profile to the continuously varying cylinder volume and perhaps adjusting that for changes in engine loading as well.
Sig Battery depleted. Reverting to safe mode.
I can see from your email address that your in the UK. In the US diesel is actually more expensive than gasoline. This is primarily due to taxes but the pricing is also influenced by refinery capacity. In any case, diesel is not substantially cheaper at the retail level.
Because there are countries like the U.S., where the infrastructure for gasoline is much better than for diesel. And diesel exhaust has more CO2 per Joule than gasoline, because longer carbohydride molecules have a higher carbon/hydrogenium ratio than the shorter ones.
Really? 99%?
Could you cite that?
Thanks.
I don't know if it actually works out to 99%, but in general, road wear rises with the 4th power of axle weight, so trucks account for the lion's share of wear and tear on roads:
http://www.pavementinteractive.org/article/equivalent-single-axle-load/
On the other hand, 99% might not be that far off: