Experimental evaluation of oxygen-enriched air and emulsified fuels in a six-cylinder diesel engine

The objectives of this investigation are to (1) determine the technical feasibility of using oxygen-enriched air to increase the efficiency of and reduce emissions from diesel engines, (2) examine the effects of water-emulsified fuel on the formation of nitrogen oxides in oxygen-enriched combustion, and (3) investigate the use of lower-grade fuels in high-speed diesel engines by emulsifying the fuel with water. These tests, completed on a Caterpillar model 3406B, six-cylinder engine are a scale-up from previous, single-cylinder-engine tests. The engine was tested with (1) intake-air oxygen levels up to 30%, (2) water content up to 20% of the fuel, (3) three fuel-injection timings, and (4) three fuel-flow rates (power levels). The Taguchi technique for experimental design was used to minimize the number of experimental points in the test matrix. Four separate test matrices were run to cover two different fuel-flow-rate strategies and two different fuels (No. 2 diesel and No. 6 diesel). A liquid-oxygen tank located outside the test cell supplied the oxygen for the tests. The only modification of the engine was installation of a pressure transducer in one cylinder. All tests were run at 1800 rpm, which corresponds to the synchronous speed of a 60-Hz generator. Test results show that oxygen enrichment results in power increases of 50% or more while significantly decreasing the levels of smoke and particulates emitted. The increase in power was accompanied by a small increase in thermal efficiency. Maximum engine power was limited by the test-cell dynamometer capacity and the capacity of the fuel-injection pump. Oxygen enrichment increases nitrogen-oxide emissions significantly. No adverse effects of oxygen enrichment on the turbocharger were observed. The engine operated successfully with No. 6 fuel, but it operated at a lower thermal efficiency and emitted more smoke and particulates than with No. 2 fuel.