Effect of LPG gas fuel injectors on the properties of low emission vehicles

Modern spark-ignition engines used for the propulsion of low emission vehicles are fuelled by injection systems in which the fuel is individually metered to each cylinder by a single injector (multipoint injection). For the proper engine operation, it is necessary that the injectors are similar to each other and stable in respect of the fuel dosage during the whole engine operation. This requirement is satisfactorily met by petrol injectors used by OEM. In contrast to petrol injectors, gas injector used in LPG-fuelled vehicles, in particular for the retrofit, are still in the development phase and therefore their quality and production consistency are often regarded as unsatisfactory from the standpoint of view of the proper engine operation. The injector-to-injector variation in the fuel dosage results in air-fuel mixture maldistribution in the cylinders, which, in turn, affects vehicle emission characteristics. The paper presents results of an investigation of inconsistency of gas injectors used in LPG vehicles in respect of their dosage. The method of measurement of the dosage uniformity is described. On the basis of the measurement, three sets of injectors differing in respect of injector-to-injector variation were selected for further vehicle tests. Tests were conducted on a passenger Euro 4 car. The emissions of limited pollutants were measured over the NEDC type-approval cycle and cycle's representative for the real world driving under Polish driving conditions. The paper presents results of the conducted tests and discusses the effect of injector-to-injector variation on the pollutant emissions.