Efficiency of a gasoline engine

Delphi Automotive is trying to develop a gasoline engine that runs like a diesel. That raises the question, why not just use diesel? According to engineers, gasoline burns cleaner, requiring less expensive emissions devices than those currently required on diesel engines.

Gasoline engines using the new technology — dubbed gasoline-direct-injection compression ignition engines — could see a 50 percent efficiency boost over conventional gasoline engines, putting them on par with gas-electric hybrids without the use of expensive battery packs and electric motors.

For those who aren't familiar with how traditional gasoline engines work, they use a spark plug (in some odd cases, more than one) to ignite a compressed air-fuel mixture in each cylinder. Diesel engines still ignite compressed air and fuel, but the mixture is compressed to higher levels than in a gasoline engine. When gasses are compressed, they heat up. Add diesel to the mixture and it explodes. To put things into perspective, a typical compression ratio for a gasoline engine is usually around 9:1, while diesel engines typically employ compression ratios anywhere from 14:1 to 25:1.

In the past, it was too difficult to control gasoline combustion in high compression diesel style engines. But current valve timing, intake and exhaust technologies have made it possible for Delphi researchers to create a one-cylinder test engine they say performs well under a variety of simulated engine conditions — idle, acceleration, load. High compression engines use fuel more efficiently than conventional gasoline engines.

Delphi engineers said they could combine their high compression gasoline engine with electric motors and batteries for even greater efficiency, but aren't sure the added cost of batteries and and electric motors would be worth it (and there's always the environmental impact of battery packs to consider). If gasoline prices jump higher over the coming years, they may see the value in a super efficient high compression gasoline-electric plugin hybrid.

But first thing's first. Delphi is currently testing multiple cylinder variants of the engine. Eventually, we'll want to see how well they perform in an actual car on the road, because there are some conditions a lab could never simulate. If they can make it work and wrap it in a sexy shell, they'll make a lot of people happy. (Hat tip to Prasan!)