A Rapid Compression Machine Study on Ignition Delay Times of Gasoline Mixtures and their Multicomponent Surrogate Fuels under Diluted and Undiluted Conditions

In this work autoignition delay times of two multi-component surrogates (high and low RON) were experimentally compared with their target full blend gasoline fuels. The study was conducted in a rapid compression machine (RCM) test facility and a direct test chamber (DTC) charge preparation approach was used for mixture preparation. Experiments were carried over the temperature range of 650K-900K and at 10 bar and 20 bar compressed pressure conditions for equivalence ratios of (Φ =) 0.6-1.3. Dilution in the reactant mixture was varied from 0% to 30% CO₂ (by mass), with the O₂:N₂ mole ratio fixed at 1:3.76. This dilution strategy emulates exhaust gas recirculation (EGR) substitution in spark ignition (SI) engines. The multicomponent surrogate captured the reactivity trends of the gasoline-air mixtures reasonably well in comparison to the single component (iso-octane) surrogate. The trends in the negative temperature coefficient (NTC) region, at both diluted and undiluted conditions, were captured well by the multi-component surrogates. The addition of diluent prolonged the ignition delay times in reference to the undiluted conditions indicating no or weak chemical reactivity due to CO₂ addition. The retarding effect of the CO₂ dilution was more pronounced in the NTC region when compared to the lower and higher temperature range.