Homogeneous charge compression ignition (HCCI) is a new
combustion concept which achieves high efficiency, low nitrogen
oxides (NOx), 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.