Investigation of diesel engine operating and injection system parameters for low noise, emissions, and fuel consumption using Taguchi methods

In order to optimize the performance of a small direct injection (DI) diesel engine with respect to noise, emissions, and fuel economy, an experimental investigation was undertaken using Taguchi methods. A single-cylinder 3.5 kW diesel engine was selected for performance tests at different levels of two operating parameters (speed and load) and six injection parameters of the engine (static injection timing, plunger diameter, nozzle valve opening pressure, nozzle hole diameter, number of nozzle holes, and nozzle tip protrusion). These controlled parameters were varied at two levels, and the resulting changes in responses were investigated, namely engine noise, combustion noise, smoke, brake specific fuel consumption (b.s.f.c.), and emissions of unburned hydrocarbons (HC), oxides of nitrogen (NOx), and carbon monoxide (CO) were investigated. The optimum values of engine noise, combustion noise, smoke, emissions, and b.s.f.c. could be predicted using signal-noise (S/N) ratios, and a relevant combination of controlled input parameters was specified. Results of confirmation runs of the engine showed good agreement with the predicted quantities of interest based on Taguchi analysis. The relative importance of the controlled parameters to the above responses was evaluated in terms of the percentage contributions of the parameters using analysis of variance (ANOVA). The Taguchi method of experimental design was found to be robust and more cost effective for understanding the relationship between diesel engine parameters and noise, emissions, and b.s.f.c. than full factorial design.