Performance and Emissions Using Water in Diesel Fuel Microemulsion 2001-01-3525

Alternative fuels providing diesel engine emission reductions are developed in order to provide practical solutions to environmental problems in different areas of the world. Diesel fuel emulsions containing water, considered as alternative fuels, have shown their potential to help reaching simultaneous reduction of NOx and PM exhaust emissions.

In this study, diesel fuel microemulsions have been developed and optimized considering their cost-effectiveness. Water is incorporated into the fuel in the form of micelle structures, mostly using naturally derived surfactants. The finished fuel is visually transparent and thermodynamically stable over a wide range of storage and handling conditions.

Experimental work was conducted to explore the impact of water in diesel fuel microemulsions on CIDI engine performance, regulated and non-regulated exhaust emissions. Engine bench-experiments and field-tests have been conducted to provide detailed information as feedback for fuel development, and also to demonstrate the benefits of the fuel technology as a retrofit option to end users.

Steady-state tests on two different engines used microemulsions prepared in fuels with aromatic contents between 8 and 25 wt %, and water incorporation varied from 10 to 17 vol %. A heavy-duty diesel engine was tested to analyze the hot-start transient emissions using a California Reference fuel as baseline, compared to microemulsions containing 12 vol % of water. In these three engines, power output changes were determined at intermediate and rated speed. Vehicle driveability and exhaust gas smoke opacity were measured on four urban buses operating at city service.

Results indicate that NOx, PM and CO can be significantly reduced because of water in diesel fuel microemulsions. Under certain conditions, the HC emissions can be increased, but this does not exceed the regulated limit for specific engines. It is noteworthy that NOx+HC emissions are effectively reduced as requested in the latest exhaust emission regulation. The non-regulated emissions determined through gas phase speciation could be controlled so as to not exceed those with the baseline fuel used to prepare the microemulsion. Power reductions can be optimized to be lower than the water volumetric content in the diesel fuel. There is evidence of improved fuel conversion efficiency in the combustion process. For in-service vehicles, adequate engine protection through improved fuel lubricity, long term fuel stability and vehicle driveability can be all completely satisfactory for end users. Exhaust emission reductions, in particular the exhaust opacity, can be visually noticeable to end users, which is quantitatively documented with actual measurements. Fuel microemulsions are shown to be a competitive alternative fuel and retrofit option to provide exhaust emission reductions in diesel engines.