Comparative Assessment for Improvement of Performance and Exhaust Emissions in Existing Dual-Fuel Diesel Engines

Abstract

Using natural gas as a supplement for the conventional diesel fuel in a compression-ignition environment—a natural gas/diesel dual-fuel (NG/DDF) engine—seems to be a solution for reducing soot and nitric oxide (NO) emissions in existing and future diesel motor vehicles. NG/DDF operation, compared with that of conventional diesel engines, suffers from higher specific energy consumption (SEC) and higher carbon monoxide (CO) and unburned hydrocarbons (HC) emissions. This seems to become more apparent at part-load operations. Diesel injection pressure (DIP) and cylinder pressure (CP) of the charge at the inlet valve closing (IVC) event (PIVC) are two critical engine parameters which affect performance characteristics and pollutants of NO, CO, and soot of a NG/DDF engine. This work studies theoretically the effects of DIP and PIVC on the performance and exhaust emissions (NO, CO, and soot) of a light-duty diesel engine operated with methane, which is the chief component of natural gas. The study is carried out using a custom-built model, which is two-zone and of the phenomenological type. The accuracy of the modeling results is tested by using corresponding experimental data acquired by an extensive experimental study performed previously on a NG/DDF engine. The primary objectives of this comparative appraisal are to specify the effects of the aforementioned parameters on the emitted pollutants and the performance characteristics of the specific engine, and to record the disadvantages and advantages. The conclusions of the specific investigation are useful, particularly to identify the optimum combination of the strategies for improving the overall performance of an existing compression-ignition (CI) engine operating with natural gas/diesel.