Dimethyl ether (DME) has very good compression ignition characteristics, and can be converted from methanol using a γ - alumina catalyst. A previous report investigated a compression ignition methanol engine with DME as an ignition improver. The results showed that the engine operation was sufficiently smooth without either spark or glow plugs. Two methods were studied, one was an aspiration method, and the other was a torch ignition chamber method (TIC method). The aspiration method allows a simple engine structure, but suffers from poor engine emissions and requires large amounts of DME. With the TIC method where the DME was introduced into a torch ignition chamber (TIC) during the intake stroke, the diffusion of the DME into the main combustion chamber was limited, and significant reductions in both the necessary quantity of DME and emissions were obtained [1][2].
In the previous experiment, the cylinder pressure could not be measured because the TIC was installed in the hole of the pressure transducer, and optimization of the TIC was not attempted.
In this study, a new TIC head, with the TIC close to the center of the main combustion chamber, was designed for the TIC method. The possibility for further improvements in reducing the quantities of DME and emissions were investigated by optimizing the TIC position, methanol injection timing, DME injection timing, and intake and exhaust throttling. It was found that the necessary amount of DME was greatly reduced when optimizing methanol and DME injection timings. Intake throttling has little effect on the reduction in the quantity of DME, but exhaust throttling can reduce the minimum amount of DME. As a result, the quantity of DME was finally reduced to 5% of the total energy supply, or 1/10 of that needed with the aspiration method over a wide range of engine operating conditions.