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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.

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.

This paper presents a new firing concept for internal combustion engines called APIR and its performances. This concept attempts to merge the best of both Compression Ignition (CI) and Spark Ignition (SI) engine worlds. The application of this concept to a standard SI engine, leads to a consequent improvement of the firing and combustion performances. 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. This paper points out that the APIR device has a lower knock sensitivity and isn't much affected by the in-cylinder aerodynamics. Thus, it can be shown that to take full advantage of the APIR concept in terms of efficiency and pollutants emissions, the SI engine must be redesigned in terms of compression ratio and in-cylinder aerodynamics.

This SI engine research investigation extends a previous study [14] concerning one kind of non-conventional firing device: the Pulsed Jet Combustion (PJC) igniter. The PJC device was compared to a conventional spark plug during operation in a 4-valve single cylinder engine at 2000 rpm and a variety of air/fuel ratios and loads. Additionally, skip-firing was used to vary the residual gas rate. The mass fraction burned intervals were calculated from the pressure trace for each cycle via a heat release analysis that accounted for cycle-to-cycle variations in the trapped mass of fuel. Statistical analyses were performed for 100 cycles of operation for each test condition. Similar results were found for the PJC device as for the spark plug with zero residual (five skipped cycles). For both igniters, the cycle-to-cycle variability increased with increasing residual, but the variability was less pronounced for the PJC device.

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.

One way of improving electronic engine control is to get an insight into the combustion process, using a direct measurement method: this means the sensor must be put straight into the combustion chamber. The reference for analyzing combustion development is the cylinder pressure sensor. Due to the price of this sensor and the added complexity for cylinder head design and manufacturing, cylinder pressure sensors are not conceivable today for mass production. An alternative to the cylinder pressure sensor is the ionization sensor. It seems to be very promising for electronic engine control. Several publications have already demonstrated the benefits of ionization currents sensing for misfire detection, knock detection, closed loop ignition control, air-fuel ratio estimation. On the contrary, other publications have shown severe limitations of the ionization sensor. For example, fuel composition or additives can influence the ionization current.