Search

This work aimed to numerically study the effect of hydrogen injection strategy on mixture formation and combustion process in a port injection (PI) rotary engine fueled with natural gas/hydrogen blends. The two main considered factors were hydrogen injection timing (IT) and hydrogen injection duration (ID). Simulation results indicated that for mixture formation, in terms of hydrogen IT, hydrogen IT of 390°CA (BTDC) is a watershed. When the hydrogen IT is before 390°CA (BTDC), the changes in hydrogen IT have little effect on the hydrogen distribution at ignition timing. Hydrogen distribution is uniform across the whole combustion chamber. However, when the hydrogen IT is after 390°CA (BTDC), with the retarded hydrogen IT, there is obvious increase in hydrogen stratification phenomenon, and more hydrogen distributes in the middle and back of combustion chamber at ignition timing. In terms of hydrogen ID, at the fixed hydrogen IT of 360°CA (BTDC), with the extended hydrogen ID, more hydrogen distributes in the back of trailing spark plug (TSP). For combustion process, to obtain a higher overall combustion rate for the PI rotary engine, the hydrogen injection strategy should make more hydrogen located at the front of TSP at ignition timing. In engineering applications, for higher peak cylinder pressure to be obtained, the continued optimization of hydrogen IT should be selected between 390°CA (BTDC) and 330°CA (BTDC). Under the hydrogen IT range of 390°CA (BTDC) to 330°CA (BTDC), the continued optimization of hydrogen ID should select between 8°CA and 24°CA. [ABSTRACT FROM AUTHOR]

Hydrogen direct injection (HDI) in cylinder is considered as an effective method to improve natural gas engine performance. The present study aims to bridge the gap on the HDI in rotary engine, and to investigate the effect of hydrogen injection timing (IT) and hydrogen injection duration (ID) on mixture formation and combustion process of a hydrogen direct injection plus natural gas port injection (HDI + NGPI) rotary engine. Numerical approach was used in this study for obtaining some critical information, which was difficult to obtain through experiment, such as flow field, fuel distribution and some intermediate concentration fields in cylinder. The research results showed that for mixture formation, the distribution law of the hydrogen and the natural gas at the late stages of the compression stroke (100 ° CA (BTDC)), was as follows: at a fixed ID of 24 ° CA, with retarded hydrogen IT, the stratification phenomenon of hydrogen became obvious increasingly, and the hydrogen distribution area moved towards the back of the combustion chamber continuously. At a fixed IT of 210 ° CA (BTDC), with the extension in ID, the accumulation area of hydrogen reduced significantly, and the hydrogen continued to gather in the middle of the combustion chamber. For combustion process, the overall combustion rate for the hydrogen injection strategy which had an IT of 210 ° CA (BTDC) and ID of 40 ° CA (case ID5), was the fastest. This was due to the fact that compared with the leading spark plug (LSP), the combustion condition around the trailing spark plug (TSP) has a great influence on the combustion process. For case ID5 at ignition timing, the hydrogen concentration near the TSP is high enough for the rapid formation of flame kernel. Compared with case IT1 which had an IT of 390 ° CA (BTDC) and an ID of 24 ° CA, the improved combustion rate of case ID5 had a 11.7% increase in peak pressure, and a 7% decrease in NO emissions. [ABSTRACT FROM AUTHOR]