Higher Efficiency Gasoline Engines

New technology that could bring higher levels of efficiency and cleanliness to internal combustion engines is getting a major boost in research activity. Researchers from General Motors, Bosch, and Stanford University have begun work on a three-year, $2.5 million program that aims to accelerate the development of Homogeneous Charge Compression Ignition (HCCI). The technology provides more efficient combustion for a variety of fuels. In a gasoline engine, this could mean improvements in fuel efficiency by 20 percent and near-zero emissions of oxides of nitrogen (NOx) and particulate matter. According to GM, HCCI can bring a diesel's 80 percent efficiency to a gasoline engine at 50 percent of the cost, without a diesel's emissions.

In an HCCI engine, fuel is uniformly mixed with air, as in a spark-ignition engine, but with a higher proportion of air to fuel. Instead of a spark plug, the mixture is compressed by the piston until rising temperatures inside the chamber ignites it spontaneously - a process similar to that used in a diesel engine, but at a much lower temperature. The lower combustion temperature, combined with the lean air/fuel ratio, virtually eliminates NOx emissions and lowers throttling losses, which leads to a significant boost in fuel economy. Sophisticated sensors, actuators, and feedback control systems that are both robust and cost-effective are required before HCCI is ready for real-world use. With the added experience of Bosch and Stanford, GM hopes to demonstrate the viability of HCCI within the next few years.