Numerical investigation of the effects of location, energy, timings, and crevices of laser ignition on the performance and emissions of a gasoline direct injection (GDI) internal combustion engine

Abstract

A gasoline direct injection (GDI) internal combustion engine was simulated with the traditional spark plug replaced by a laser pulse ignition. This was performed by setting the spark energy, ignition time, and energy transmission to the gases to match those of a laser ignition system. The simulations were conducted on ANSYS Forte and using the integrated chemistry solver CHEMKIN-Pro. This work aims to continue the previously conducted research at the University of Balamand while introducing a crevice model and studying the effects of varying the laser energy, timing, and location on the performance and Hydrocarbon (HC), CO, and NOx emissions at different engine speeds. A numerical analysis was performed on various sets of energies, locations, and timings at two equivalence ratios 𝜙=0.6 and 𝜙=0.8, reflecting the range of equivalence ratios for DI engine operations. A mesh sensitivity analysis was conducted in order to identify the minimum required mesh density and it was determined to be 0.3 centimeters. Laser energy variation consisted of simulating the effects of using a base energy value and comparing it to double, 4 times and 8 times that value. Performance and emissions did not benefit from the changes in laser energy for both equivalence ratios with increases of up to 30% in NOx. A comparison between the non-crevice and crevice model was also performed and analyzed deeming the crevice model used logical and the results significant as CO and UHC levels increased significantly showing differences as high as 12,000% compared to the non-crevice model. The laser energy variation was conducted for both equivalence ratios with the crevice model on at engine speeds of 1,500 and 3,000 rpm, showing again no benefits in terms of performance and emissions. Laser location was also studied. In this case the configurations were two narrowly distanced simultaneous ignition points; two widely distanced simultaneous ignition points; double centrally located pulsing phased by 2 crank angle degrees; and finally, a multiple location pulsing phased by 4 crank angle degrees which was determined for each speed and equivalence ratio by analyzing the equivalence ratio distribution before ignition in order to decide on the optimum locations and sequence of ignition. The results favored a different configuration for each equivalence ratio and engine speed. Gross indicated power increased by up to 7.2% with burning of up to 80% of the UHC compared to the base cases. Results showed no benefits in changing the laser energy while each equivalence ratio and engine speed had a specific laser configuration which yielded the best overall performance and stability with a reduction in emissions. It was concluded that laser ignition offered the ability to run engines at lean equivalence ratios hence improving their efficiency and stability while reducing emissions. Faster flame propagation results in higher peak temperatures sometimes increasing NOx concentration but reducing UHC in the chamber. Future work and fine tuning of the timings and location of ignition could lead to promising results and show clear benefits to using laser ignition.