Tomorrow's engines could boast greater fuel efficiency and lower emissions because of a system being developed by Oak Ridge National Laboratory. New ORNL test data shows that spark-assisted homogeneous charge compression ignition has a 12 percent improvement in fuel efficiency and a 95 percent reduction in nitrogen oxide emissions compared to conventional spark ignition. ORNL plans to marry this concept with the rotating arc spark plug, which was invented at ORNL. The new engine will be a hybrid of conventional spark ignition and the compression ignition process that takes place in spark and diesel engines and normally results in engine knock. The key to increased efficiency is that burning of the fuel takes place faster inside the cylinder, allowing energy extraction for the full piston stroke. Controlling this process and eliminating the knocking sound has always been difficult, but the addition of spark assist using the rotating arc spark plug should improve stability and transient control.
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