Members of the GM's HCCI team preparing a prototype engine for testing.
The battle between the Otto cycle and the Diesel cycle in auto engines goes back more than 100 years. Diesels have a fuel economy advantage, roughly 20%, compared to traditional gasoline engines largely because of a higher compression ratio needed to ignite the fuel and the elimination of “pumping losses” caused during the intake stroke of a gasoline engine when it is operating at partial throttle.
However, the fuel injection system of a diesel and the heavier components required to hold up to the higher pressures make it much more expensive – these days thousands of dollars more – than a gasoline engine. Tighter emissions laws on cancer-causing particulate matter are adding to the expense and reducing fuel economy. Also, diesel fuel doesn’t ignite as readily as gasoline, which makes cold starting problematic.
As automakers continue the unending quest for greater fuel efficiency, a hybrid combination of diesel and gasoline engines is being studied to see if the best characteristics of both can be obtained.
One such initiative is going on at General Motors where a homogenous charge compression ignition (HCCI) engine is under study. An HCCI engine, when combined with other advanced technologies, can provide up to 15% greater fuel economy than a comparable, non-HCCI engine by using the diesel combustion process.
“HCCI delivers enhanced fuel savings without sacrificing the performance consumers have come to expect,” said Dr. Uwe Grebe, executive director for GM Powertrain Advanced Engineering. (more…)