Investigation of the Chemical Effect of Pilot Injection on Main Combustion in a Gasoline Controlled Auto-Ignition Engine by In-Cylinder Measurements and Numerical Simulation of H2O2, HO2, and OH

• Applicants: Professor Dr.-Ing. Hans-Jürgen Koß; Professor Dr.-Ing. Stefan Pischinger
• Subject Area: Hydraulic and Turbo Engines and Piston Engines
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 389807373

Controlled auto-ignition (CAI), homogeneous charge compression-ignition (HCCI), and gasoline controlled auto-ignition (GCAI) combustion represents a technology that can reduce both NOx emissions and fuel consumption of gasoline engines as well as NOx and particulate emissions of diesel engines. However, the difficulty in controlling auto-ignition and pressure-rise rate in CAI/HCCI/GCAI engines continues to be an important issue. In the proposed project, the understanding of the chemical effect of pilot injection (PI) on main combustion will be improved. For this purpose, reactive species formed by PI such as H2O2, HO2, and OH are proposed to be experimentally probed and numerically simulated. It will also be proposed to investigate the effect of these species on main-combustion phasing and pressure-rise rate in the second funding period, i.e., the second year. The measurement of H2O2 will be attempted by photo-fragmentation laser-induced fluorescence (PFLIF), particularly in the early compression stroke of an optical GCAI engine. Potential PFLIF signal contributions by HO2 and OH will be quantified by 3D-CFD (three dimensional computational fluid dynamics) in-cylinder reactive flow simulations, as well as other potential precursors to OH. Signal contributions by PFLIF and OH-LIF are proposed to be separated by experimental means. It will be attempted to produce approximately homogeneous species distributions in the cylinder. This will be verified by spatially resolved PFLIF/ LIF (laser-induced fluorescence) measurements. If homogenous H2O2 fields are established and PFLIF signal contributions by HO2 are negligible, it will be proposed to quantify the total amount of H2O2 experimentally in the entire cylinder within the second funding period. It is a major objective of the proposed project to answer the following questions within the first funding period: Can H2O2 be measured selectively by PFLIF in the early compression stroke? Are PFLIF signals strong enough for spatially resolved and/or single-shot measurements? Can this be conducted under relevant engine operating conditions?If H2O2 (or HO2/OH) can be measured selectively under relevant operating conditions with approximately homogeneous species distributions in the early compression stroke, it will be proposed to answer the following questions in the second funding period (among others):Is H2O2 measured by PFLIF a good indicator of the chemical effect of PI on main auto-ignition? Is H2O2 the decisive species produced by PI that 'triggers' main combustion? How important are intermediate-temperature reactions compared to high-temperature combustion during re-compression for the chemical effect of PI? What is the effect of mixture homogenization during re-compression? Can combustion instabilities, such as cycle-to-cycle variations, drifting combustion phasing, and prior-cycle effects, be explained by the considered species?

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Gerd Grünefeld