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The emissions from a direct injection diesel engine measured according to the ECE R49 13-mode cycle and as a function of exhaust gas recirculation are compared for diesel fuel without water addition, and for water-in-diesel as emulsion and microemulsion. The effect of water addition on the soot emissions was remarkably strong for both the emulsion and microemulsion fuels. The average weighted soot emission values for the 13-mode cycle were 0.0024 and 0.0023 g/kWh for the two most interesting emulsion and microemulsion fuels tested, respectively; 5-fold lower than the US 2007 emission limit.

This paper presents an investigation of the effects of varying needle opening pressure (NOP) (375 to 1750 bar), engine speed (1000 rpm to 1800 rpm), and exhaust gas recirculation (EGR) (0% to 20 %) on the combustion process, exhaust emissions, and fuel consumption at low (25 %) and medium (50 %) loads in a single cylinder heavy duty DI diesel research engine with a displacement of 2.02 l. The engine was equipped with an advanced two-actuator E3 Electronic Unit Injector (EUI) from Delphi Diesel, with a maximum injection pressure of 2000 bar. In previous versions of the EUI system, the peak injection pressure was a function of the injection duration, cam lift, and cam rate. The advanced EUI system allows electronic control of the needle opening and closing. This facilitates the generation of high injection pressures, independently of load and speed.

The effects of EGR on diesel combustion were visually examined in a single-cylinder heavy duty research engine with a low compression ratio, low swirl, a CR fuel injection system and an eight-orifice nozzle. Optical access was primarily obtained through the cylinder head. The effects of EGR were found to be significant. NOx emissions were reduced from over 500 ppm at 0% EGR to 5 ppm at 55% EGR. At higher levels of EGR (approximately 35% or more) there was a loss in efficiency. Constant fuel masses were injected. Results from the optical measurements and global emission data were compared in order to obtain a better understanding of the spray behaviour and mixing process. Optical measurements provide fundamental insights by visualizing air motion and combustion behaviour. The NOx reductions observed might be explained by reductions in oxygen concentration associated with the increases in EGR.