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This paper evaluates the potential of adding simulated reformer gases in a spark-ignition engine to improve the global performances and pollutant emissions. The global composition of the simulated reformer gas is 24% CO -31% H2 - 45% N2 and the quantity of reformer gas added in the engine is varied from 0% to 50%. For all working conditions, the Indicated Mean Effective Pressure is kept constant equal to 3 bars. Intake pressure and ignition timing are adjusted to optimize the coefficient of variation of the Indicated Mean Effective Pressure. Engine performances and pollutants emissions are analysed to point out the best working conditions.

This paper follows a former one (Robinet [1]) which underlined the spark kernel hazardous development due to residual gas in the spark plug vicinity. A new igniter called FSP (Fueled Spark Plug) has been designed and compared to conventional spark plug. Its purpose is to sweep away the residual gas from the spark vicinity. This investigation has been performed in a standard research engine and an optical accesses engine. A faster heat release development and a more repeatable combustion for low-load operating conditions have been observed when firing with the FSP. The lean operating range is extended. The idle performances (IMEP covariance, ISC) have been improved as well as the emissions (CO and NOX). Unburned hydrocarbons emissions are raised due to non-optimal feed line design. Contrary to previous alternative igniter designs, residual gas sweeping can be switched on or off at will: in the latter case the FSP falls back to conventional spark plug operation.

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.