Homogeneous Charge Compression Ignition Combustion Characteristics of n-Heptane in Pure Oxygen Atmosphere

Abstract:

Based on a two-cylinder diesel engine and a self-designed pure oxygen intake system，the effect of different intake oxygen volume fractions on the combustion process and stability of homogeneous charge compression ignition of n-heptane were investigated.The experimental results show that， with the decreasing volume fraction of oxygen and increasing volume fraction of carbon dioxide in the mixture， the average specific heat capacity in the cylinder is increased， which leads to the maximum combustion temperature in the cylinder is decreased， the corresponding peak phase is delayed， the combustion start point is delayed， the peak heat release rate is decreased， and the thermal efficiency is reduced.Meanwhile， it was found that with the increasing of carbon dioxide volume fraction， the temperature in the cylinder decreased， which led to the strengthening of the combustion cycle instability. The above phenomena indicate that the higher volume fraction of carbon dioxide can effectively inhibit the homogeneous charge compression ignition of n-heptane under pure oxygen atmosphere.Moreover， the interval duration of negative temperature coefficient of n-heptane homogeneous charge compression ignition is significantly shortened in pure oxygen atmosphere.

Key words:diesel engine;n-heptane;homogeneous charge compression ignition;oxy-fuel combustion