While diesel power is our dig here, it deserved some print that GM is working on a new technology that can almost be called a combination of diesel combustion practice in a gasoline engine. The result is a gasoline engine that uses high compression without a spark.
Called “homogenous charge compression ignition” or HCCI, heat and pressure within an HCCI engine’s cylinders are used to ignite the air/fuel mixture without the aid of a traditional spark-generated flame. A spark plug is used when the engine is cold to generate heat within the cylinders and instigate “auto-ignition” of the mixture, but is phased out after warm up.
HCCI has been successfully demonstrated in prototype models in the last year. Journalists and others were even given the chance to drive them last year around the country. GM is continuing to work on this new technology that may be the next evolution of gasoline internal combustion engines to help achieve the new CAFÉ and emissions standards coming in 2016.
The increase in the HCCI operating range of the prototype vehicle is the result of a patented mixed-mode calibration that includes pre-reacting fuel and exhaust gas in the cylinder to bolster the pressure and heat needed for auto-ignition.
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. During HCCI mode, the engine approaches the efficiency of a diesel, but unlike a diesel, it requires only a conventional exhaust system. As we know, diesel engines require more after treatment to reduce emissions.
The success of HCCI development, to date, is tempered by challenges that must be overcome before it hits the primetime of production. Control of the combustion process over the wide range of operating conditions experienced in everyday driving is the greatest challenge, because unlike a conventional-ignition engine, HCCI’s combustion is not controlled by precisely timed spark events. Ensuring auto ignition at extreme temperatures and in the thinner air of high altitudes are the tallest hurdles to overcome.