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

Abstract

The results of a previous study, part 1, showed that use of a shield can improve the thermal performance of a glow plug, and thereby reduce ignition time. However, the part 1 study also found that use of a simple shield with only one circular opening can delay flame propagation out of the shield. The conclusions of that study suggested that there is scope for further improvements of the shield design, especially the shield opening geometry. Accordingly, this article presents the results of computational studies investigating the influence of multi-opening shield designs on natural gas ignition characteristics in glow plug–assisted compression–ignition engines. Two types of multi-opening glow plug shield, consisting of four small circular openings distributed in either diamond-pattern or square-pattern arrangements, were employed. The simulated results demonstrated that both multi-opening shields can not only increase glow plug surface temperature, but also increase the residence time of fuel mixture adjacent to the glow plug surface in the early injection stage, resulting in a faster ignition than the single-opening shield. Furthermore, the diamond-pattern multi-opening glow plug shield provides a faster or comparable flame propagation path back to combustion chamber, compared to single-opening glow plug shield, while the square-pattern multi-opening glow plug shield delays the flame propagation under several specific engine conditions. Compared to the single-opening glow plug shield, the overall natural gas ignition delays are further reduced by 6%–44% when using the diamond-pattern multi-opening glow plug shield, while the square-pattern multi-opening glow plug shield is only able to reduce the natural gas ignition delay under a few specific conditions.

Problems with glow plug – a review

“…Pan et al [66] studied the effect of multi-opening shield designs on natural gas ignition characteristics in glow plugassisted CI engines. Two types of multi-opening glow plug shield with four small circular openings distributed in either diamond-pattern or square-pattern arrangements, were elaborated.…”

The effect of high-pressure injection variations on the mixing state of underexpanded methane jets

“…In applying the threshold value to a single-pulse data image, however, the volume integrated intensity calculated from equation (3) is not corresponding to the injected fuel mass any longer, but a reduced fuel mass must be considered. This is illustrated in Figure 3(a), where the black dotted line marks the single-shot jet contour resulting from a 0.2 kg/m 3 threshold, while the red line represents the boundaries for the target margin of 0.6 kg/m 3 .…”

“…In compression-ignition (CI) natural gas engines an ignition assist mechanism is required, which usually comes in the form of a highcetane fuel pilot injection, although other options such as hot surface ignition have also been explored. [1][2][3] In the dual-fuel mode, the inherently higher thermal efficiency of the conventional CI engine is maintained, while NO x , PM, and CO 2 emissions are reduced. 1,4 If the gaseous fuel is inducted into the intake manifold to mix uniformly with air via the so-called port injection (PI), the displacement of air by natural gas leads to lower thermal efficiency and power output.…”

Soot and combustion models for direct-injection natural gas engines

“…Ignition by hot surface, such as a glow plug (GP), allows 100% natural gas injection in a CI engine to achieve a diesel-equivalent engine efficiency, and has been widely investigated by many laboratories. 3,4,[18][19][20][21][22][23][24][25][26][27][28][29] GP ignition eliminates the need for a complex and therefore expensive two-fuel injector as well as any contribution of the diesel pilot to emissions. The need for storing two fuels on board a vehicle is also eliminated.…”