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 the potential to offer an enhanced NOx-particulate matter 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 fuels and the impact of initial pressure and temperature on the autoignition behavior over a range of equivalence ratios. Gasolines with research octane numbers (RON) varying from 60 to 92 were investigated. The simulation results were then used to generate thermodynamic maps of ignitability for the fuels.

A Lagrangian-Eulerian modeling approach with Reynolds-Averaged Navier-Stokes (RANS) formulation was used for the 3-D CFD simulations. The CFD model validation was performed against experimental results from a 6-cylinder, 15 L heavy duty diesel engine 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 on the effect of injection strategy on engine performance and emissions. Closed-cycle 3-D CFD simulations were then carried out at the same cold idle condition for model validation and evaluation. The comparisons with the measured engine in-cylinder pressure, heat release rate, and emissions 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 these cold conditions by investigating the sensitivity of thermal boundary conditions and spray model constants.