LES Analysis of Mixture Formation and Combustion Processes in a Diesel Spray

The effects of dwell time on the mixture formation and combustion processes of diesel spray are investigated experimentally. A commercial multihole injector with a 0.123 mm hole diameter is used to inject the fuel. The injection procedure is either a single or split injection with different dwell times, whereas the total amount of injected fuel mass is 5.0 mg per hole. Three dwell times are selected, that is, 0.12, 0.32 and 0.54 ms, with a split ratio of 7:3 based on previous findings. The vapour phase is observed, and the mixture formation pertaining to the equivalence ratio is analysed using the tracer laser absorption scattering (LAS) technique. A high-speed video camera is used to visualise the spray combustion flame luminosity, whereas a two-colour pyrometer system is used to evaluate the soot concentrations and flame temperature. An analysis of the mixture formation based on the spray evaporating condition reveals a more concentrated area of the rich mixture within a 0.32 ms dwell time. In the shortest dwell time of 0.12 ms, the equivalence ratio distribution decreases uniformly from the rich mixture region to the lean mixture region. In the case involving a shorter dwell time, a suitable position for the second injection around the boundaries of the first injection is obtained by smoothly growing the lean mixture and avoiding the large zone of the rich mixture. Therefore, the shortest dwell time is acceptable for mixture formation, considering the overall distribution of the equivalence ratios. Spray combustion analysis results show that the soot formation rate of the single injection and 0.32 ms dwell time case is high and decreases quickly, implying a rapid reduction in the high amount of soot. Consequently, 0.12 ms can be considered the optimal dwell time due to the ignition delay and relatively low soot emission afforded.

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Effect of split injection on mixture formation and combustion processes of diesel spray injected into two-dimensional piston cavity

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1177/0954407017724246 ◽

2017 ◽

Vol 232 (8) ◽

pp. 1121-1136 ◽

Cited By ~ 5

Author(s):

Kang Yang ◽

Hirotaka Yamakawa ◽

Keiya Nishida ◽

Youichi Ogata ◽

Yusuke Nishioka

Keyword(s):

Soot Formation ◽

Single Injection ◽

Injection Pressure ◽

Diesel Spray ◽

Two Dimensional ◽

Mixture Formation ◽

Split Injection ◽

Main Injection ◽

Combustion Processes ◽

Injection Strategies

The objective of this study is to obtain an enhanced understanding of the effect of split injection on mixture formation and combustion processes of diesel spray. A two-dimensional (2D) piston cavity of the same shape as that used in a small-bore diesel engine was employed to form the impinging spray flame. The fuel was injected into a high pressure, high temperature constant volume vessel through a single-hole nozzle with a hole diameter of 0.11 mm. The injection process comprised a pre-injection followed by the main injection. The main injection was carried out either as a single injection of injection pressure 100 MPa (Pre+S100), or by two types of split injection of injection pressure 160 MPa. The latter two types were defined by mass fraction ratios 1:1 and 3:1 (Pre+D160_1-1, Pre+D160_3-1). In order to observe the spray mixture formation process, the tracer laser absorption scattering (LAS) techique was adopted. Tracer LAS fuel with 97.5 vol% of n-tridecane and 2.5 vol% of 1-methylnaphthalene (α-MN) was employed. The spatial distributions of the vapor and liquid phases and the spray mixture formation characteristics in the 2D piston cavity for the three injection strategies were investigated. The diesel spray combustion and soot formation processes were studied using a high-speed video camera. The flame structure and soot formation process were examined using two-color pyrometry. The experimental results revealed that the split-injection vapor distribution was significantly more homogeneous than that of the single injection. The main injection fuel caught up with the pre-injection fuel and provided the spray tip with substantial additional momentum, enabling it to advance further. A high soot concentration and low temperatures appeared near the cavity wall region under the three injection strategies. The soot reduction rate for split injection was higher than that for single injection. The second main injection caught up with the previous injection’s flame, which deteriorated the combustion and resulted in higher soot generation. The effect of split injection on the process of soot evolution finished at the same time as that of single injection.

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LES Analysis of Mixture Formation and Ignition in a Diesel Spray

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.78.652 ◽

2012 ◽

Vol 78 (787) ◽

pp. 652-662 ◽

Cited By ~ 1

Author(s):

Hirokazu KOJIMA ◽

Hiroshi KAWANABE ◽

Takuji ISHIYAMA

Keyword(s):

Diesel Spray ◽

Mixture Formation

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Characteristics of Diesel Spray With Varying Injection Rate

ASME 2019 Internal Combustion Engine Division Fall Technical Conference ◽

10.1115/icef2019-7242 ◽

2019 ◽

Author(s):

Intarat Naruemon ◽

Long Liu ◽

Dai Liu ◽

Xiuzhen Ma

Keyword(s):

Ignition Time ◽

Fuel Mixture ◽

Injection Rate ◽

Diesel Spray ◽

Low Temperature Combustion ◽

Multiple Injection ◽

Injection Duration ◽

Injection Process ◽

Temperature Combustion ◽

Combustion Processes

Abstract Multiple-injection is an effective injection strategy in order to control the advanced combustion processes in diesel engines. However, because of the multiple-injection application, cause the duration of each injection is shortened, such as the pilot injection and post-injection. The short injection duration results in a very short quasi-steady injection process so that the ramping-up and ramping-down injection processes occupied a much larger scale during the injection. As a result, this circumstance of the spray evolution not been fully understood. To investigate the diesel spray propagation with varying injection rate, visual experiments and numerical simulation analyses on diesel spray were performed. The penetrations of diesel sprays with short injection duration were obtained by reflected shadowgraphy in a combustion chamber’s constant-volume with the multi-hole injector. The diesel spray with varying injection rates was modeled by using CONVERGE CFD software and the model was calibrated and validated by the experimental data. Then diagnosed the spray characteristics including spray penetration, Sauter means diameter, as well as fuel concentration distribution, were analyzed with different injection quantities and injection rate shapes. The spray mixing analysis included that after the end-of-injection in order to consider the low-temperature combustion phenomenon. The shape of the improved injection rate in the fuel mixture considered in the case of injection ending before or after the ignition time was summarized for different conditions.

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