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The principle of combustion stimulation by a gas jet is to inject a small amount of the incombustible gas in the SI engine combustion chamber. Depending on the moment of the gas injection with respect to the moment of the spark ignition, the jet (introduced in the right direction) stirs unburned charge (injection before ignition) or goes through the flame kernel (injection after ignition) and removes chemically active combustion products towards farther parts of the chamber. Previous investigations revealed that in both cases the jet can result in combustion intensification, in increase of the indicated mean effective pressure (IMEP) and in significant increase of the cycle peak pressure. Besides, the action of the gas jet can affect knocking combustion, cyclic variability and can decrease pollutant emissions. Previous investigations explained, by means of visualisation of the combustion process, the mechanism of most of the phenomena caused by the gas jet.

Results of experimental studies of the JDC (Jet Dispersion Combustion) method to stimulate burning in SI piston engines are presented. The principle of the method is to disperse combustion gases originated from the homogeneous charge flame kernel throughout whole combustion chamber by means of the gas jet introduced in the chamber from outside. Emphasis is placed on relationships between system parameters and pollutant emissions. Results of exhaust gas composition measurements are presented at various jet directions. In general, at any engine load, the external air injection tends to decrease CO and HC contents in the exhaust gas, and NOx concentration remains basically unchanged. At idling conditions, it was possible to decrease remarkably CO concentration (even below 0.2 % by volume) without increasing HC and NOx levels. The measured exhaust gas composition was strongly dependent on the injection direction.

The results of the application of the Jet Dispersed Combustion (JDC) method [6] to an actual piston engine are presented. The influence of the gas (air) jet action introduced dynamically in the engine combustion chamber on pressure traces is demonstrated, for various jet directions. The investigations revealed significant positive influence of the injection on the pressure profiles at various engine operational conditions. The results of the investigations confirmed that the promising features of the JDC method, observed before at the conditions being far from engine reality, can be utilized in the actual engine. The attempts to explain the combustion mechanism introduced by the JDC method are also reported.