Laminar Burning Velocity of Premixed Ethanol-Air Mixtures with Laser-Induced Spark Ignition Using the Constant-Volume Method

Ethanol is a widely used gasoline alternative because of its renewability. Laser-induced spark ignition (LISI) is a promising ignition technique for internal combustion engines because of its advanced lean-burning capability and flexibility in ignition location and energy. However, determining laminar burning velocities of ethanol-air mixtures with LISI is difficult because of its irregular three-lobe flame profile. In this paper, LISI and spark ignition (SI) were used to ignite premixed ethanol-air mixtures in a constant-volume combustion chamber at the initial temperature and pressure of 358 K and 0.1 MPa, respectively. The constant-volume method (CVM), which uses pressure history data as inputs rather than flame images as in the constant-pressure method (CPM), was applied for LISI to overcome the aforementioned issue. Additionally, two chemical kinetic mechanisms were used to obtain simulated laminar burning velocities. When SI is used, laminar burning velocities obtained from the CVM were 1.1-6.3% higher than those from the CPM. This was due to some assumptions made in the CVM. When applying LISI and CVM, the laminar burning velocities were obtained over a wide range of pressures (0.1-0.3 MPa) using extrapolation. As the pressure was extrapolated to two times of the initial pressure (0.2 MPa), the largest and the mean deviations between the laminar burning velocities obtained from the CVM and the simulation were approximately 10 and 5%, respectively. As the pressure was extrapolated to a higher pressure (0.3 MPa), a larger deviation was observed. Therefore, the laminar burning velocities obtained in this study between the initial pressures of 0.1 and 0.2 MPa are reliable.