August 12, 2009
Supercritical Diesel 10% More Efficient
Thought diesel efficiency might be topping out already? Apparently not. Internal combustion engines still have more room for improvement.
Researchers in New York have demonstrated a supercritical diesel fuel-injection system that can reduce engine emissions by 80 percent and increase overall efficiency by 10 percent.
With the approach of Peak Oil we need every advantage we can find with fuel efficiency. 95% of all transportation energy comes from oil. So the transportation sector is most vulnerable to high oil prices.
I hope they can combine that with this. And fit it on a scooter. We will see.
The funny thing about Infernal Combustion Engine technology is that there are zillions of ways to improve it, and every year there are many proposals for new ICE tech. Wankel rotary engines are a famous example, but there are zillions more.
Almost all of them die because the improvements aren't quite enough to justify the enormous cost of introducing a new engine design and scaling up production to get economies of scale. The same things happens everywhere in the economy. For instance, Firefly's new-gen lead-acid battery is having trouble getting traction, because li-ion is accepted as the Next Big Thing in batteries. The US DOD is supporting Firefly, so it may make it - an example of a beneficial government intervention.
There's a rule of thumb for innovation: it can't be 10% better, or twice as good, it has to be 10x as good as the status quo in order to succeed. This may overstate things a bit, but it gives a good flavor for the challenges involved.
The problem with the supercritical diesel is that the raw fuel cokes at its critical temperature. It requires the addition of a diluent such as CO2 to make it stable in the supercritical state. I did not see any figures on the energy cost of recovering CO2 from engine exhaust to close the loop, and carrying CO2 would increase the fuel weight and net emissions considerably. Further, there are easier ways to get a 10% improvement in most vehicles; just changing the engine operating point to higher torque at lower RPM can double efficiency for many vehicles.
If this scheme allows unconventional fuels such as raw pyrolysis oil to be used in diesels, that may be worth it.
Your suggesting that people will tank a diesel/CO2 mix.
ps. If they use the CO2 from the refinery it won't increase the net emissions
That would require capture, storage, shipping and fuelling of CO2 along with the petro-fraction. Even assuming that there's enough (I would bet that this scheme would improve gasoline efficiency also), it would be a big investment in new pipelines, tank farms and high-pressure tankers, plus a lot of added weight and bulk on the vehicles. Supercritical water might be a better choice of diluent if exhaust recovery of CO2 is not feasible; the methanol or ethanol you'd need for antifreeze can come from biomass or be generated from NG or LPG.
How much CO2 would you need per liter?
Hmmm. I mis-read the TR article; apparently the work uses exhaust gas as the diluent, not some purified fraction thereof. That makes it a lot easier.