Combustion improvement and pollutants reduction with diesel-gasoline blends by means of a highly tunable laser plasma induced ignition system

The use of alternative fuels in compression ignition engines, either completely or partially replacing the conventional ones, have potential to reduce pollutant emissions (especially soot). However, some of these fuels do not provide good ignition features under diesel engine like conditions, which affects engine efficiency. Thus, in order to extend the application of alternative fuels, the current research proposes the use of a laser induced plasma ignition system to assist on the combustion of blends of fuels with less reactivity than pure diesel. This fuel has been chosen as the base component and it has been mixed with gasoline (as the low-reactivity fuel) in different ratios as an example of fuels with very different reactivity properties. Tests have been performed in a single cylinder optically accessible engine, allowing deeper study of combustion development and soot formation. For different in-cylinder conditions and fuel blends, the effect of laser induced plasma ignition system has been evaluated at different crank angle degrees and locations inside the combustion chamber. The application of these blends under low-reactivity engine conditions show that combustion efficiency is dramatically affected. However, the study proves that it is possible to control blend ignition delay and flame lift-off length by means of laser induced plasma. Besides, using the proper ignition system configuration, combustion characteristics similar to those of diesel fuel autoignition can be achieved for high gasoline substitution rates. They lead to similar energy release rates, which confirms that diesel-gasoline blends can reach a combustion efficiency close to pure diesel, while a strong reduction on soot formation was also obtained. These results open a door to efficiency improvement and pollutant reduction by means of a highly tunable ignition of alternative fuel blends.