Numerical Evaluation of Gasoline Compression Ignition at Cold Conditions in a Heavy-Duty Diesel Engine 2020-01-0778
Achieving robust ignitability for compression ignition of diesel engines at cold conditions is traditionally challenging due to insufficient fuel vaporization, heavy wall impingement, and thick wall films. Gasoline compression ignition (GCI) has shown good potential to offer enhanced NOx-soot tradeoff with diesel-like fuel efficiency, but it is unknown how the volatility and reactivity of the fuel will affect ignition under very cold conditions. Therefore, it is important to investigate the impact of fuel physical and chemical properties on ignition under pressures and temperatures relevant to practical engine operating conditions during cold weather. In this paper, 0-D and 3-D computational fluid dynamics (CFD) simulations of GCI combustion at cold conditions were performed.
First, 0-D simulations were performed to evaluate the ignitability of different gasoline-like fuels and the impact of initial pressure and temperature on the autoignition behavior over a range of equivalence ratios and anti-knock indices (AKI). Gasolines with research octane numbers (RON) varied from 60 to 92 were investigated. The simulation results were then used to generate thermodynamic maps for ignitability for the different gasolines.
A Lagrangian-Eulerian modeling approach with Reynolds-Averaged Navier-Stokes (RANS) formulation was used for 3-D CFD combustion simulations. CFD Model validation was performed against experimental results from a six-cylinder, 15 L heavy duty diesel engine. The engine was operated at a compression ratio (CR) of 17.3 and a 600 rpm cold idle condition using a RON92 E0 gasoline. Experiments have also been conducted to study the effect of injection strategy on engine performance and emissions. Closed-cycle 3-D CFD simulations were carried out at the above-mentioned experimental operating points for model validation and evaluation. The comparisons with the measured engine in-cylinder pressure, heat release rate, and emissions at all operating conditions showed that the CFD model results were generally in good agreement with the experiments. Experimentally validated CFD simulations were further used to gain insight into the spray, ignition and combustion processes for GCI under the cold operations by investigating the sensitivity towards thermal boundary conditions and spray model constants.
Le Zhao, Muhsin Ameen, Yuanjiang Pei, Yu Zhang, Praveen Kumar, Tom Tzanetakis, Michael Traver
Argonne National Laboratory, Aramco Research Center