Effect of water - methanol blends on engine performance at borderline knock conditions in gasoline direct injection engines

One of the limiting factors improving the efficiency of gasoline engines is engine knock. Various techniques including using fuels that result in charge cooling are employed to mitigate knock and improve efficiency. Water and methanol have higher heat of vaporization than gasoline. When water or methanol is injected into the intake manifold, it evaporates by exchanging energy with the charge mixture resulting in charge cooling. This allows the engine to be run with advanced spark timing without engine knock. With this motive, the impact of water - methanol injection on the engine performance of a gasoline direct injection engine was investigated. Experimental studies were conducted on a single-cylinder 0.55L engine with a compression ratio of 10.9:1 at 800 kPa net indicated mean effective pressure and 1500 revolutions per minute. Baseline tests without water injection were conducted by direct injection of gasoline fuel blended with 10% ethanol (E10). Four mixtures: 100% water, 75% water + 25% methanol, 50% water + 50% methanol and 100% methanol were used with port injection. Spark ignition timing, flow rate of the fuel and the four mixtures were varied to be within the controlled knock limit while maintaining an excess air ratio of 1.0. Comparisons on the effectiveness of these mixtures indicate that higher methanol content in the mixture helped in reaching the maximum brake torque condition at lower mixture fuel ratios. Combustion stability of the engine was improved with the addition of water and water-methanol blends due to the sensitivity of combustion phasing at advanced spark timings reducing the variation in indicated mean effective pressure. Exhaust gas temperatures decrease with the addition of water and water-methanol blends due to the combined effect of increased charge cooling and improved combustion phasing.