Pryor lit himself on fire well before HCCI
As Triumph the Comic Insult Dog would say, “I keed, I keed.” The groundbreaking comic is not speaking from the grave and homogenous charge compression ignition (HCCI) is actually a pretty big deal. As you may know, diesel engines are more efficient than equivalent gasoline engines. A good rule of thumb is that all things being equal, a diesel engine will provide roughly a thirty percent boost in fuel economy over its gasoline counterpart. Diesel engines operate differently than gasoline engines in that they ignite the air/fuel mixture without the aid of a traditional spark-generated flame. You might be familiar with ‘dieseling’ gasoline engines continuing to run after the key has been turned off. In fact, a dieseling gasoline engine is not using compression to ignite the fuel but rather a hot spot in the cylinder, but the concept is the similar: there is no spark igniting the mixture.
What HCCI does is try to mimic a diesel engine by using heat and pressure to ignite the air/fuel mixture. HCCI’s efficiency comes from reduced pumping losses, burning fuel faster at lower temperatures and reducing the heat energy lost during the combustion process. Consequently, less carbon dioxide is released because the engine’s operation in HCCI mode is more efficient. Plus you don’t get a nasty smell on your hands or unwilling have to consort with truckers at the diesel pumps (I say unwillingly because I know that there are folks who willingly consort with truckers at truck stops, not that there is anything wrong with that).
During HCCI mode, the engine approaches the efficiency of a diesel, but unlike a diesel, it requires only a conventional exhaust system. Diesel engines require more elaborate and more expensive exhaust “aftertreatment” to reduce emissions. So HCCI gives you fuel economy that rivals a diesel for a fraction of the cost, sounds great, right? The problem is, conditions have to be optimal and a sophisticated engine management system has to ride herd over the whole setup or you’ll end up sounding something like this. An HCCI engine starts up using a spark ignition and runs that way until the motor is at the proper temperature when it then switches over to compression ignition. Drivers who have had some seat time in HCCI equipped vehicles report that the transition between HCCI and spark ignition is audible but otherwise seamless. What GM is trying to do is expand the operating range that HCCI can work under so that efficiency can be maximized.
Keep your eyes peeled for HCCI as it has the potential to be a game changer. GM isn’t the only company working on HCCI, rest assured it’s an industry wide preoccupation. Undoubtedly HCCI, especially when combined with other fuel saving technology, will deliver us to the promised land of wondrous fuel economy without regressing to Pinto levels of acceleration.