Abstract
Keywords
Diesel injection, High pressure injection, HEUI, Smoke emissions, NOx emissions.
Abstract
Optimisation of the combustion process is still one of the most important methods of improving diesel engine emissions, the fuel injection equipment being central to this process. The present paper reports research using a new HEUI, single fluid injector currently under development by Enviro Diesel Systems, Pty Ltd (EDS) in Australia with the support of the IC Engines Laboratory, University of New South Wales (UNSW). The HEUI is a single fluid preliminary metering type designed for diesel engines of up to 1.3 litre/cyl. Preliminary metering allows a spill port to terminate injection giving a very fast, clean cut-off. A medium pressure common rail fuel accumulator supplies the HEUI which uses a standard nozzle and has independent electronic control of the injection timing, fuel delivery and maximum injection pressure. A preliminary pulse and/or slope variation of the leading from of the injection curve can be incorporated. These parameters, including the slope, are independent of engine speed. The HEUI has now achieved a maximum injection pressure of 230 MPa and, for fuel injection down to 40% of maximum delivery, injection pressures can be set anywhere in the range from 35 MPa to over 200 MPa. At the low end, a delivery of less than 1% maximum is achievable, still with high injection pressure.
Tests at full load show, with increasing injection pressure and maximum cylinder pressure held constant by ignition timing alterations, that a substantial reduction in smoke emissions occurs, that NOx increases and ISFC is lower. The lowest injection pressure is taken as the baseline. By retarding the timing, the NOx can be held at, or reduced below, the baseline values with the smoke levels still being improved significantly. At the high speeds, injection pressure had a noticeable effect on NOx but a relatively insignificant one at low speeds. Other low speed trends followed those at high speed. When at part load IMEP is held to that of the original mechanical, in-line pump injection system on the same engine, the higher injection pressures of the HEUI improve smoke and ISFC value. If NOx is held the same or reduced below that of the in-line system, the smoke can again be noticeably reduced.