GM Rethinks Engine With Homogeneous Charge-Compression Ignition:
Dismissed as a laboratory curiosity in the 1970s, homogeneous charge-compression ignition (HCCI) has now emerged as a more feasible alternative to alternative fuels — and it’s almost ready to roll out en masse. When used in conjunction with other advanced engine technologies, this combustion process can help deliver a whopping 25- to 30 -percent better fuel economy than today’s spark- or compression-ignited internal combustion engines (ICE). HCCI does all this with near-zero emissions, just like a hybrid — and it won’t have any impact on your driving habits or come at a premium price.
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So what makes the HCCI process different from spark or compression ignition? It delivers a more complete, efficient burn at temperatures too low for the formation of harmful nitrous oxides. As a result, the job of cleaning the exhaust becomes much easier, resulting in fewer greenhouse gases being expelled into the atmosphere. It also requires a much leaner air/fuel mixture (less fuel, more air) for detonation than in a standard four-stroke engine — hence the 25- to 30- percent bump in fuel economy. Plus, burning gasoline at a lower temperature means that considerably less energy is lost through the exhaust pipe, or transferred as waste heat into the engine’s cooling system.Originally known as active thermo-atmosphere combustion, HCCI was first discovered in 1979 by engineers at the Nippon Clean Engine Research Institute in Japan trying to perfect a cleaner, more efficient two-stroke engine. But at the time HCCI couldn’t be controlled well enough to work in a four-stroke engine. Advances in microprocessors, sensors and control systems have somewhat rectified that problem, sending nearly every top-tier carmaker (notably GM with the process explained above, Honda with activated radical combustion and Mercedes-Benz with its DiesOtto program) as well as a consortium of U.S. universities and government labs (recently contracted by the Department of Energy) into overdrive as they scramble to perfect an engine that employs HCCI.
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