Page 1 of 12 SAE Technical Paper 2010-01-0615 PERFORMANCES AND EMISSIONS IMPROVEMENT OF AN S.I. ENGINE FUELLED BY LPG/GASOLINE MIXTURES Emiliano Pipitone, Stefano Beccari Department of Mechanics, University of Palermo Copyright © 2010 SAE International DOI: 10.4271/2010-01-0615 ABSTRACT As is known gaseous fuels, such as Liquefied Petroleum Gas (LPG) and Natural Gas (NG), thanks to their good mixing capabilities, allow complete and cleaner combustion than normal gasoline, resulting in lower pollutant emissions and particulate matter. Some of the automobile producers already put on the market “bi-fuel” engines, which may be fed either with standard gasoline or with LPG. These engines, endowed of two separate injection systems, are originally designed for gasoline operation; hence they do not fully exploit the good qualities of LPG, such as its better knocking resistance, which would allow higher compression ratios. Moreover, when running with gasoline at medium high loads, the engine is often operated with rich mixture and low spark advance (with respect to the maximum brake torque value) in order to prevent from dangerous knocking phenomena: this produces both high hydrocarbon and carbon monoxide emissions and high fuel consumption. Starting from these observations, the authors experimentally investigated on the simultaneous combustion of LPG- gasoline mixtures in stoichiometric proportion with air (with different LPG/gasoline mass ratios), so as to exploit the good qualities of both fuels to obtain cleaner and more efficient combustions: the addition of LPG to the gasoline-air mixture in fact raises knocking resistance, allowing thus to run the engine with both “overall stoichiometric” mixture and more efficient spark advance even at full load, while the stoichiometric A/F ratio allows to minimize pollutant emissions. In this paper the authors present the results of an extensive experimental study in terms of engine efficiency increments and reduction of pollutant emissions with respect to the pure gasoline operation. INTRODUCTION Automobile market is nowadays characterized by a great diffusion of bi-fuels vehicles, i.e. vehicles endowed of Spark Ignition (SI) engines which can be run either on standard gasoline or on gaseous fuels, such as Natural Gas (NG) or LPG (Liquefied Petroleum Gas). With respect to conventional fuels, besides a lower price, these gaseous fuels also exhibit lower pollutant emissions, and this in turn makes bi-fuels vehicles suited for the urban centre transportation. However, current bi-fuel vehicles are equipped with SI engines developed for the use with gasoline, and are not optimized for LPG or natural gas. Moreover, when running with standard gasoline, these engines are usually operated with rich mixtures and poor spark advance in order to prevent dangerous knocking phenomena: these cause both high fuel consumption and high Carbon Monoxide (CO) and Hydrocarbons (HC) emissions, as shown in Figure 1, which reports with continuous lines, the emissions levels measured at full load by a series production bi-fuel engine, while, for a comparison, the dashed lines represent the probable pollutant concentrations which would be measured running the engine with stoichiometric mixtures.