Influence of the Spatial and Temporal Interaction Between Diesel Pilot and Directly Injected Natural Gas Jet on Ignition and Combustion Characteristics

Abstract

In this paper, pilot-ignited high pressure dual-fuel combustion of a natural gas jet is investigated on a fundamental basis by applying two separate single-hole injectors to a rapid compression expansion machine (RCEM). A Shadowgraphy system is used for optical observations, and the combustion progress is assessed in terms of heat release rates (HRRs). The experiments focus on the combined influence of injection timing and geometrical jet arrangement on the jet interaction and the impact on the combustion process. In a first step, the operational range for successful pilot self-ignition and transition to natural gas jet combustion is determined, and the restricting phenomena are identified by analyzing the shadowgraph images. Within this range, the combustion process is assessed by evaluation of ignition delays and HRRs. Strong interaction is found to delay or even prohibit pilot ignition, while it facilitates a fast and stable onset of the gas jet combustion. Furthermore, it is shown that the HRR is governed by the time of ignition with respect to the start of natural gas injection—as this parameter defines the level of premixing. Evaluation of the time of gas jet ignition within the operability map can therefore directly link a certain spatial and temporal interaction to the resulting heat release characteristics. It is finally shown that controlling the HRR through injection timing variation is limited for a certain angle between the two jets.

A Review of Hydrogen Direct Injection for Internal Combustion Engines: Towards Carbon-Free Combustion

“…Under an assumption that a maximized overlapping of diesel and gas jets after the auto-ignition of diesel fuel will yield the best performance, a converging injector configuration with small angle (a few degrees) was recommended [88]. The effect of the dual-fuel jet interaction under engine-relevant reactive conditions was studied by Fink et al [89,90] in a RCEM. Different injector orientations were used to change the degree of jet interaction-the gas injection angle was changed by rotating the injector while the diesel jet was fixed.…”

“…The injection pressure limit of the HPDI 2.0 system is around 600 bar for both diesel and CNG. Previous studies [89,90] employed a prototype injector by L'Orange from Germany to inject CNG at high pressure of up to 330 bar. However, no information about the applicability of this prototype for hydrogen injection is available.…”

Heat release rate and emissions regimes of stratified pilot-ignited direct-injection natural gas combustion

“…In addition to the NG stratification, several studies have concluded that complex interactions between the NG jet and pilot jet and ignition are critical to PIDING combustion performance. 27–29 Using a rapid compression-expansion machine (RCEM), Fink et al 28 demonstrated that for positive RIT where pilot ignition occurs undisturbed by the NG jet, a wide range of relative spray angles can be used to produce robust NG ignition. However, when there is temporal overlap of the pilot and NG jets (i.e.…”

Parametric Study of Autoigniting Hydrogen–Methane Jets in Direct-Injection Engine Conditions

“…After autoignition, the initial AHRR during the premixed combustion phase is associated with the flame spreading across the readily mixed jet volume. The AHRR during the mixing-controlled combustion phase after the premixed period is correlated with the fuel–air mixing rate. ,, For the ambient temperature cases, it can be seen that the AHRR rises rapidly after ignition, which is followed by a stabilization period as the flame develops into a quasi-steady diffusion flame. The peak AHRR increases with a lower temperature case that has a longer ignition delay and, therefore, additional mixing to produce a higher volume of the readily combustible mixture at ignition.…”