An experimental study of HCCI-DI combustion and emissions in a diesel engine with dual fuel

An experimental study of port injected n-heptane homogeneous charge compression ignition (HCCI) in combination with in-cylinder diesel fuel direct injection (DI) was conducted on a single cylinder diesel engine. By adjusting the quantities of premixed n-heptane as well as the direct injected diesel fuel, different premixed ratios were obtained over a wide range of load conditions while the test engine was kept at a constant speed. The effects of premixed ratio (rp) and direct injection timing on HCCI-DI combustion characteristics and emissions were investigated. In order to evaluate the traits of HCCI-DI combustion, the conventional diesel and HCCI engine performances were presented to be compared with their results. Furthermore, special emphasis was put on the combined combustion process analysis. It can be found that the NOx emissions decreased dramatically with partial premixing and it exhibited a descending trend as a function of rp increase when the rp was lower than 0.3, but it showed a great tendency to increase when the premixed ratio was higher. The inherent trade-off of NOx and soot was not obvious since the soot emissions remained at the same level of the prototype diesel engine under the condition of lower rp. Moreover, the influence of rp on the CO and UHC emissions was assessed. The results also revealed that the HCCI-DI combustion could effectively improve the indicated thermal efficiency of diesel engine at low to medium loads.