Evaluation of the Efficiency of a Double Spark Plug to Improve the Performances of Combustion Engines: Pressure Measurement and Plasma Investigations

The ignition sparks provided by the conventional spark plug (CSP) do not always ensure a fast and complete combustion of the hydrocarbon–air mixture. For this reason, we offer a new type of spark plug with two simultaneous discharges generated by a pulsed high voltage–power supply. First, we present results concerning geometrical and electrical characteristics of plasmas produced in air and in engine combustion chamber. A more important volume of plasma is highlighted. The larger surface of interaction of plasma with the air-to-fuel mixture promotes the initiation of a greater number of chemical reactions thus increases the rate of propagation of the combustion. In addition, for long pulse durations the energy delivered by the double spark plug (DSP) to the discharge is 20% higher, as compared to a CSP. The current rise rate is more important for the DSP, which allows better ionization of the mixture. Afterwards, we present a study of two four-strokes engines ignited by this DSP, one powered with gasoline and the second one with propane. The pressure into the cylinder, measured as a function of the crankshaft angle, allowed to compute the IMEP, COVIMEP, and PPP, for both tested engines. In the case of the gasoline engine, when the ignition and flame development conditions are difficult—a high ignition angle was considered—the DSP can offer an almost 3.5 times better operation stability (considering the coefficient of variation of the indicated mean effective pressure as main indicator) and a faster development of the combustion flame (defined by the means of the pressure peak position). A study was also performed as a function of the equivalence ratio for the propane-powered engine, which confirmed the results regarding the DSP performances obtained with the first engine. In addition, this study highlighted that for very lean mixtures, the DSP can provide a better stability in operation (COVIMEP, COVPPP) is assured even for equivalence ratios in the range of 0.65, where the use of CSPs involves misfires and very high engine vibrations.