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The paper presents a new firing concept for internal combustion engines. This concept attempts to merge the best of both Spark Ignition and Compression Ignition engine worlds. The concept is called APIR in French, standing for ‘Auto-inflammation Pilotée par Injection de Radicaux’, meaning Self-ignition Triggered by Radical Injection. The application of this concept to a standard SI engine, leads to a consequent improvement of the firing and combustion performances. A dramatic cycle variability decrease is pointed out. Initiation and combustion develop with a speed and a repeatability incomparable with the spark plug firing case. The use of the APIR device leads to an increase of the engine operating range in terms of Lean Operating Limit and thus Lean Burn Torque Range. An interesting gain on fuel consumption for idle and low load operating points is pointed out.

This paper reports on an experimental investigation of an SI single cylinder engine cycle-to-cycle variations. Two different ignition devices are studied: a spark plug and a non conventional ignition device, PJC (Pulsed Jet Combustion). In-cylinder pressure is analyzed via a complete heat release rate computation. A significant decrease in IMEP cycle-to-cycle variations can be achieved only when the initial burning rate is enhanced with PJC device for example. The cycle-to-cycle combustion variations (CA01, PMax, IMEP) are not improved in the same proportions. The PJC is a firing device which meets the objective of repeatable ultra-lean mixture ignition and development of combustion, but slightly lowers the global efficiency due to the increase of heat losses for high load running points.