Characteristics of a spark ignition engine operated with adulterated fuel : combustion, particulate matter and polycyclic aromatic hydrocarbons

Abstract

Fuel adulteration is a widespread problem in South Asian countries, some forms of which are responsible for deterioration in performance and increase in emissions of spark ignition (SI) engines. A common form of adulteration is to blend gasoline with kerosene which is prevalent because of financial benefit resulting from the price difference between the two fuels. The current study involves the use of known gasoline-kerosene blends to fuel a single cylinder Ricardo E6 engine and study the combustion characteristics and emissions of such blends. At non-knocking conditions, the combustion parameters including cylinder pressure, mass fraction burned and heat release rates, do not show any significant difference between gasoline and the blends. However, as the spark timing is advanced, the kerosene blends start knocking earlier than gasoline. This study compared both the knock intensity and knocking tendency of gasoline and the blends using various available methods. All the techniques of knock characterisation confirm that increasing the amount of kerosene in the blend increases knocking tendency and its intensity. Further, detailed analysis of knock pressure signals showed that the maximum heat release rate during knock cannot be correlated with knock intensity as some previous authors have suggested. Emissions including total hydrocarbon (THC), particulate matter (PM) and polycyclic aromatic hydrocarbon (PAH) were investigated in the present study considering the fact that blending kerosene reduces volatility of the fuel which would increase those emissions. Results show significant increases in these potentially harmful emissions even with moderate amounts (10-20% by volume) of kerosene in the blend. With 20% kerosene in the blend, the PM and PAH increase by about two times or more at an equivalence ratio 1 and over, compared to gasoline fuelling. Comparison of fuel PAH and emitted PAH revealed that some P AH are formed entirely during the combustion process and some PAH were present in the exhaust at higher amount compared with the fuel PAH concentration. Further, the variation of particulate phase PAH emissions closely resembled the PM emissions as the fuel type and operating conditions are varied. It was seen that the conditions that favoured PM emissions also favoured PAH emissions.