The effect of 2-ethyl-hexyl nitrate on HCCI combustion properties to compensate ethanol addition to gasoline

Stable HCCI combustion requires a proper level of fuel reactivity. This study shows that adding ethanol as a renewable fraction to low octane gasoline decreases the reactivity of the gasoline, while adding 2-ethyl hexyl nitrate (2-EHN) can enhance the reactivity of the blend and counter the effect of ethanol. The experimental apparatus consisted of a modified CFR engine for HCCI combustion equipped with two port fuel injectors and an intake air heater. Gasoline blended with ethanol (10% v/v) was used as the base fuel. Different percentages of 2-EHN (0.25%, 0.50%, 1%, and 2.5%) were added to the base fuel as an ignition improver. The blends were tested at operating points defined for HCCI number at two different engine speeds (600 and 900 rpm) and three different intake temperatures (50, 100, and 150 degrees C) to investigate the effect of 2EHN on the auto-ignition behavior of the fuel. Combustion, emissions, and performance parameters of HCCI combustion of the blends were measured. The presence of 2-EHN in the blends improved the auto-ignitability of the blends in a nonlinear manner. It was also found that 0.25% of 2-EHN can compensate for the effect of ethanol on the required compression ratio and remove the quenching effect of ethanol on low temperature heat release. The results show that for the same fuel, a higher compression ratio is needed to maintain the combustion phasing constant at a higher engine speed.