Abstract: The combustion of gasoline-air mixtures in a constant-volume combustion chamber with an initial condition of 0.1 MPa pressure and 363 K temperature is experimentally investigated with laser ignition generated by a Q-switched Nd:YAG laser (wavelengths of 532 and 1064 nm). Spark ignition is also tested, and the results are used as the benchmark. Combustion chamber pressure is measured by a piezoelectric pressure transducer, and recorded using a digital oscilloscope. When the equivalence ratio is swept from 1.2 to 1.8, laser and spark ignition show marginal differences in pressure rise rate and peak pressure. The maximum pressure rise rate and the maximum peak pressure are obtained at equivalence ratios of 1.6 and 1.8 for laser ignition and spark ignition, which are 39.4 MPa/μs and 0.68 MPa for the laser wavelength of 532 nm, 38.8 MPa/μs and 0.67 MPa for the laser wavelength of 1064 nm, and 38.1 MPa/μs and 0.67 MPa for spark ignition, respectively. When the equivalence ratio is reduced below 1.2, the pressure rise rate and peak pressure of the laser ignition are significantly higher than those of spark ignition, and the lean limit for laser ignition is also wider than that of spark ignition; therefore, laser ignition is more favorable for lean combustion. For both the laser and spark ignitions, the ignition energy demonstrated a limited impact on both the pressure rise rate and peak pressure. Heat release rate in the combustion chamber is calculated, and the results show that variations of heat release are in accordance with variations of the pressure history.

Key words: Laser ignition, Spark ignition, Pressure rise rate, Peak pressure, Heat release rate

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