Numerical studies of the ignition characteristics of a high-pressure gas jet in compression-ignition engines with glow plug ignition assist: Part 1—Operating condition study

Abstract

This article presents the results of computational studies investigating the ignition of high-pressure natural gas jets in a compression-ignition engine with glow plug ignition assist. The simulation was conducted using a KIVA-3V-based three-dimensional engine model, along with an improved fuel injector model, a detailed cut-off glow plug shield model and a modified two-step methane reaction mechanism, to simulate the natural gas injection and ignition. The simulated results demonstrate the significance of using a shield for the glow plug. Compared to an unshielded (bare) glow plug, the shield not only reduces the heat loss from the hot glow plug surface to the cold intake air charge and the cold injected gas jet but also traps the fuel mixture to increase its residence time adjacent to the hot surface. Over a representative range of heavy-duty diesel engine operating conditions, a shielded glow plug greatly improves the natural gas engine performance and provides reliable ignition, while an unshielded glow plug can only be optimized for specific conditions. The understanding of glow plug shield behavior gained from the simulations suggests avenues for improved shield designs that would yield further reduced ignition delays.

Numerical studies of the ignition characteristics of a high-pressure gas jet in compression ignition engines with glow plug ignition assist: Part 2-Effects of multi-opening glow plug shields

“…Based on this engine configuration, a KIVA computational model was developed to represent only the geometry and structure of the CFR engine’s external combustion chamber, 38,44–47 where the fuel injection and ignition occurred, as shown in Figure 2(b). The engine model has been validated by experimental data 48,49 that indicates the computational model can well simulate the jet penetration, fuel mixing, and hence ignition and flame propagation.…”

“…Employing a shield can insulate the GP from the cooling flows of intake air and the subsequent injected natural gas jets. 38–43 Part 1 of this study 38 was a simulation that validated that a shielded GP can improve the ignition stability over a full range of engine operating conditions. However, the part 1 simulations also showed that flame propagation out of the shield will sometimes be delayed under several operating conditions when injecting the fuel jets onto a GP employing a shield with a single circular opening.…”

“…However, the part 1 simulations also showed that flame propagation out of the shield will sometimes be delayed under several operating conditions when injecting the fuel jets onto a GP employing a shield with a single circular opening. 38 Since the shield opening is the only route for fuel flowing into the GP shield and the primary route for flame propagation out, the optimization of shield design was studied in the current work, Part 2, using a computational engine model 38 to investigate further means of reducing ignition delay.…”

“…This study was carried out to explore arrangements of multiple openings that might minimize the time required for the ignited mixture to propagate from the shield into the main combustion chamber. Two different designs, created by distributing four small circular openings with different patterns on the GP shield, were simulated using the natural gas engine model, 38 and the results were compared to the single-opening GP shield. Ignition performance under different engine combustion chamber configurations, for example, various fuel injection angles and GP surface temperatures, and under different engine operating conditions, for example, various engine speeds and loads, was evaluated.…”

A quasi-one-dimensional model for an outwardly opening poppet-type direct gas injector for internal combustion engines

“…Catapano et al 20 experimentally optimized the injection process in an SI DI-CNG engine to reduce the coefficient of variation (CoV) of combustion and improve the power output. Pan and Wallace 21,22 studied the ignition characteristics of high-pressure gas jets in the context of compression ignition (CI) engines using a cylindrical nozzle design for the direct injector. In the very recent experimental investigations of CI DI-CNG engine, Rochussen et al 23 performed a parametric study of NG combustion in an optical heavy-duty engine.…”