Spray and Combustion Characteristics of HCCI Engine Using DME/Diesel Blended Fuel by Port-Injection

摘要

Homogeneous charge compression ignition (HCCI) is a new combustion concept which achieves high efficiency, low nitrogen oxides (NO_x), and particulates matter (PM) emissions. In order to realize the HCCI combustion, a homogenous mixture preparation plays an important role in the HCCI engine. However, it is well known that diesel fuel is very difficult to achieve a uniform mixture distribution within the engine cylinder because of its high viscosity and poor fuel vaporization. In order to eliminate these problems, the low viscosity and high volatility Dimethyl ether (DME) was added into diesel fuel to enhance the spray and atomization. The spray tip penetration and spray cone angle of DME/diesel-blended fuel has been examined by using direct photography technology. Measurements were achieved by using spray images taken with a high-resolution CCD camera synchronized with strobe light. Results obtained reveal that the spray behavior and atomization are enhanced with the increase in DME ratio. Accordingly, the DME/diesel-blended fuel was injected into the manifold near the intake port by using pintle type injection nozzle. Then the fuel/air mixture was sucked into the cylinder, and HCCI combustion can be fulfilled. The premixed ratio of DME/diesel-blended fuel was estimated with various DME ratios, different intake temperature and injection pressure on a modified single-cylinder diesel engine. Based on the optimal parameters of DME to diesel ratio and injection pressure, the combustion and emission characteristics are investigated for the diesel/DME HCCI engine at different intake air temperature.