Experimental Study of Autoignition Characteristics of the Ethanol Effect on Biodiesel/n-Heptane Blend in a Motored Engine and a Constant-Volume Combustion Chamber

To explore the effect of the addition of ethanol (E) on the combustion behavior of biodiesel/n-heptane (BH) blends, autoignition characteristics of the BHE blends were studied in two experimental systems: a modified cooperative fuel research (CFR) engine and a constant-volume combustion chamber (CID 510) used for rating the derived cetane number of fuels. The observations of ignition behavior include the critical compression ratio and heat release profile, which are assessed using the CFR engine. The equivalence ratio is 0.25 and 0.45, respectively, while the physical and chemical ignition delays are measured by the CID 510 under a wide range of air temperatures and oxygen dilution levels. With the addition of the ethanol, the critical compression ratio increases, which indicates that the reactivity decreases. According to the heat profiles, because of the complex composition of the blend, the onset of the high temperature heat release (HTHR) and low temperature heat release (LTHR) did not vary linearly w...