Experimental comparison of combustion and emission characteristics between a market gasoline and its surrogate

Mixtures of few representative hydrocarbon species are often used in computational studies as surrogates of market petroleum fuels, which contain hundreds of components. While this simplification is imperative for computational costs of reaction kinetics, it introduces unavoidably uncertainties in simulations. Differences between the real and the surrogate fuels regarding mixture formation, oxidation chemistry, and fuel composition contribute to such uncertainties. An evaluation of the underlying concept of a surrogate fuel model in terms of engine performance is thus of high interest. This paper presents an experimental study with a spark-ignition (SI) single-cylinder engine (SCE) to compare the combustion and emission characteristics between a market gasoline fuel and its corresponding four-component surrogate (iso-octane, n-heptane, toluene, ethanol). The measurements cover a wide range of operating points in terms of engine load, speed, air-to-fuel ratio, and operating conditions. Together with standard performance and emission measurements, a non-standard hydrocarbons (HC) analysis has been performed with a fast flame ionization detector and an ion-molecule-reaction mass spectrometer. The comparison reveals very good agreement between the market gasoline and the surrogate fuel regarding combustion and global gaseous emission behaviors, with an average deviation for almost all of the analyzed quantities below 2%. The comparison of CO emissions in stoichiometric operation presents a higher scatter, due to the high sensitivity of the CO emissions on mixture formation and fuel volatility. The different compositions of the two fuels also lead to deviations of speciated-HC emissions, which is confirmed by mass spectrometry. Additionally, the sooting tendency of the surrogate fuel is found to be more than 10 times lower compared to the market gasoline fuel.