ULEV Potential of a DI/TCI Diesel Passenger Car Engine Operated on Dimethyl Ether

The paper describes a feasibility test program on a 2 liter, 4 cylinder DI/TCI passenger car engine operated on the new alternative fuel Dimethyl Ether (DME, CH₃ - O - CH₃) with the aim of demonstrating its potential of meeting ULEV emissions (0.2 g/mi NOx in the FTP 75 test cycle) when installed in a full size passenger car. Special attention is drawn to the fuel injection equipment (FIE) as well as combustion system requirements towards the reduction of NOx and combustion noise while keeping energetic fuel consumption at the level of the baseline DI/TCI diesel engine. FIE and combustion system parameters were optimized on the steady state dynamometer by variation of a number of parameters, such as rate of injection, number of nozzle holes, compression ratio, piston bowl shape and exhaust gas recirculation. The paper presents engine test results achieved with DME under various operating conditions and compares these results to those achieved with the diesel version of the same engine. The FTP 75 cycle results were projected from steady state engine maps using a vehicle simulation program taking into account vehicle data and road resistance data of a given vehicle. The cycle results are also compared to actual chassis dynamometer results achieved with the diesel version of the same engine installed in the same vehicle. The passenger car DI/TCI engine adapted for and operated on DME shows very promising results with respect to meeting ULEV NOx emissions without any soot emissions and without the need for a DENOX catalyst. DME fuel consumption on energy basis can be kept very close to the DI diesel value. An oxidation catalyst will be necessary to meet the stringent CO and HC ULEV emission limits.