0D/1D Turbulent Combustion Model Assessment from an Ultra-Lean Spark Ignition Engine 2019-01-1409
This paper focuses on the assessment of a predictive combustion model using a 0D/1D simulation tool under high load, different excess air ratio λ , and different combustion stabilities (based on the coefficient of variation of indicated mean effective pressure COVimep). To consider that, crank angle resolved data of experimental pressure of 500 cycles are recorded under engine speed 1000 RPM and 2000 RPM, wide-open throttle, and λ=1.0, 1.42, 1.7, and 2.0. Firstly, model calibration is conducted using 18 cases at 2000 RPM using 500 cycle-averaged in-cylinder pressure to find optimized model constants. Then the model constants are unchanged for the other cases. Next, different cycle-averaged pressure data are used as inputs in the simulation model based on the combustion stability COVimep in order to study sensitivity of turbulent model constant.
The simulation is conducted using one-dimensional simulation software GT-Power. Firstly, a three-pressure analysis model (intake, in-cylinder, exhaust) for experimental prediction and optimization of burn rate shape are studied. Boundary conditions such as the three pressure histories, intake/exhaust valves timing, boundary temperature, and exhaust gas emissions are used as inputs. Errors of indicated thermal efficiency, indicated mean effective pressure, and CA50 are within 3%. Predicted parameters from the three-pressure analysis model such as air volumetric efficiency, trapped air/fuel vapor mass, trapped residual gas fraction, tumble, and surface temperature of the piston, head, and valves are used as initialization in the predictive combustion model. A built-in flame propagation model, termed as SITurb, is investigated whether it can replicate the in-cylinder pressure and burn rate shapes. A revised laminar flame speed correlation of five-component gasoline surrogate is incorporated in the combustion model via an encrypted dynamic link library file. The results show the thermodynamic histories of the combustion are reproducible under high load and stoichiometric-to-ultra-lean conditions. Under all cases, only turbulent flame speed multiplier needs to be calibrated.
Ratnak Sok, Kyohei Yamaguchi, Jin Kusaka