A comparison of water-diesel emulsion and timed injection of water into the intake manifold of a diesel engine for simultaneous control of NO and smoke emissions

Experiments were conducted to compare the effects of water-diesel emulsion and water injection into the intake manifold on performance, combustion and emission characteristics of a DI diesel engine under similar operating conditions. The water to diesel ratio for the emulsion was 0.4:1 by mass. The same water-diesel ratio was maintained for water injection method in order to assess both potential benefits. All tests were done at the constant speed of 1500 rpm at different outputs. The static injection timing of 23 degrees BTDC was kept as constant for all experimental tests. In the first phase, experiments were carried out to asses the performance, combustion and emission characteristics of the engine using the water-diesel emulsion. The emulsion was prepared using the surfactant of HLB:7. The emulsion was injected using the conventional injection system during the compression stroke. The second phase of work was that water was injected into the intake manifold of the engine using an auxiliary injector during the suction stroke. An electronic control unit (ECU) was developed to control the injector operation such as start of injection and water injection duration with respect to the desired crank angle. The experimental result indicates the both methods (emulsion and injection) could reduce NO emission drastically in diesel engines. At full load, NO emission decreased drastically from 1034 ppm with base diesel to 645 ppm with emulsion and 643 ppm with injection. But, NO emission reduction is lesser with injection than emulsion at part loads. Smoke emission is lower with the emulsion (2.7 BSU) than with water injection (3.2 BSU) as compared to base diesel (3.6 BSU). However, CO and HC levels were higher with emulsion than water injection. As regards NO and smoke reduction, the emulsion was superior to injection at all loads. Peak pressure, ignition delay and maximum rate of pressure rise were lesser with water injection as compared to the emulsion. It is well demonstrated through this comparative study that the emulsion method has higher potential of simultaneous reduction of NO and smoke emissions at all loads than injection method. (C) 2010 Elsevier Ltd. All rights reserved.