Conventional versus sparkless ignition - Image courtesy of GM
A few years ago sparkless ignition or homogeneous charge compression ignition (HCCI) in gasoline engines was all the rage, with a number of major automakers including General Motors, Daimler and Volkswagen all investigating its benefits.
Since then, not much has been heard of the technology whereas hybridization and full electrification of the vehicle has grown in popularity.
It appears HCCI technology still has a bright future as automotive supply giant Bosch, together with a number of partners and a $12 million grant from the U.S. Department of Energy, is working on a commercially viable HCCI engine.
HCCI works by achieving combustion with only compression of the air-fuel mix rather than using a spark plug--something that diesels already do. However, in gasoline engines designers are faced with a number of challenges.
The biggest challenge of HCCI in gasoline engines is controlling the combustion process. With spark ignition, the timing of the combustion can be easily adjusted by the powertrain control module, with control of the spark event. That is not possible with HCCI's flameless combustion.
The mixture composition and temperature must be changed in a complex and timely manner to achieve comparable performance of spark-ignition engines in the wide range of operating conditions. That includes extreme temperatures--both hot and cold--as well as the thin-air effect of high-altitude driving.
To overcome this, designers could use an engine that uses gasoline but switches between spark ignition and diesel-style compression ignition when required, reports Automotive News (subscription required).
If successful, Bosch estimates that a gasoline engine with HCCI and existing technologies such as turbocharging and stop-start systems could be up to 30 percent more fuel efficient than a conventional engine of the same performance.
Its first prototype engine will be a 2.0-liter GM Ecotec unit fitted with a supercharger, a turbocharger, direct fuel injection, a stop-start system, variable valve timing, and HCCI compatibility. Researchers hope their prototype will be as powerful as GM’s 3.6-liter V-6 but with the 30 percent target for a reduction in fuel consumption.
Unfortunately, the technology still appears to be in its early days as the prototype engine won't be completed until some time in 2014, meaning any commercial release may not appear until closer to the end of the decade.