PERFORMANCE AND EMISSIONS OF A CI ENGINE FUELED WITH WATER IN DIESEL EMULSION THROUGH MICROCHANNELS EMULSIFICATION

This paper reports the results of an experimental investigation carried out on a prototype optically accessible compression ignition engine fuelled with water in diesel emulsion (WiDE). The effect of WiDE on combustion process evolution and exhaust emissions was investigated through standard engine benchmark and optical diagnostics, providing the lack of literature on the topic. WiDE might be one of the potential approaches to reduce emissions in compression ignition engines improving the NOx-Soot trade-off. The cooling effect of water evaporation reduces the in-cylinder temperature. The difference between water and diesel evaporation rate promotes the micro-explosion of water droplets trapped in the emulsion, with air-fuel mixing improvement that results in soot reduction. The emulsion was produced through a prototype designed microchannels emulsifier. The water concentration was 9.1%v with a small amount (0,2%v) of nonionic surfactant (SPAN80) used to stabilize the emulsion. 2D chemiluminescent emission measurements were carried out during the whole combustion process using a Charge-Coupled Device (CCD) camera coupled with a band-pass filter centred at 690 nm, to discriminate the soot emission from other excited chemical species. Tests were performed comparing combustion and exhaust emissions of the reference commercial diesel fuel to the WiDE. A single injection strategy was selected and the start of injection (SOI) was swept from 8 to 23 CAD BTDC. For the diesel case, the whole amount of injected fuel and injection pressure were set at 22 mg/str and 80 MPa, respectively, corresponding to a medium load regime for an automotive light duty diesel engine. For any investigated fuel and operating point, engine tests were carried out changing the injection interval to achieve the same chemical energy as the reference diesel (935 J/str). Compared to Diesel, the WiDE induced an increase in ignition time, enhancing the air/fuel mixing with a simultaneous reduction in both PM and NOx. The digital imaging and 2D chemiluminescence techniques highlighted a reduction in soot formation without significant changes on the soot oxidation rate. The results suggest the WiDE as a reliable technique to improve NOx-soot trade-off of CI engines.