Reducing Emissions and Controlling Combustion Phasing in HCCI Engines

Direct-injection compression-ignition engines also known as HCCI (homogeneous charge compression-ignition) engines offer an alternative to conventional spark-ignited and diesel combustion systems. HCCI engines produce low particulate (soot) and nitrogen oxide emissions and exhibit high thermal efficiency. However in HCCI engines there is no direct control of ignition such as a spark. Instead HCCI engines rely on auto-ignition making combustion phasing (timing of auto-ignition) difficult to control. UW-Madison researchers have now developed a method to effectively control combustion phasing in direct-injection compression-ignition engines by using suitably timed multiple fuel injections. In this technique an initial fuel pulse is injected during the early phase of the compression stroke. The pulse is timed to mix with cylinder air so that it is too “lean” to produce appreciable soot and nitrogen oxides upon combustion but not so lean that it creates significant amounts of unburned hydrocarbons and carbon monoxide. Normally the pulse is also too lean to auto-ignite leading to problems with combustion phasing. To solve this the researchers inject a second fuel pulse that provides a locally rich fuel mixture for effective auto-ignition. They have optimized the second injection’s timing and amount to reduce the soot and nitrogen oxides normally resulting from a single late fuel injection. Technology Applications: 1) Gasoline engines 2) Diesel engines