28권 4호 247-254 2020 [한국자동차공학회 논문집 ]
| 제목 | 천연가스의 고압 간접 분사에 따른 과소 팽창 제트의 충격파 구조와 천이 거동에 관한 수치적 연구 |
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| 분야 | 연료 및 배기 |
| 언어 | Korean |
| 저자 | 문성준(한국자동차연구원), 정수진(한국자동차연구원) |
| Key Words | Compressed natural gas engine(압축천연가스엔진), Under-expanded nozzle(과소 팽창 노즐), Under-expanded jetsjets(과소 팽창 제트), Shock waves(충격파), Shock cell(충격파 셀), Transitional behavior(천이 거동), Detached eddy simulation(분리 와류 모사) |
| 초록 |
To maximize the combustion efficiency of manifold port injection for the CNG(compressed natural gas) engine, the gaseous fuel should be injected at a high pressure using a gas injector, which allows for sufficient fuel supply and good mixture formation n the cylinder. In particular, the increase of the NPR(nozzle pressure ratio) because of the high-pressure injection causes shockwave formation near the nozzle exit as well as a change in the shock patterns in the gas jet. The characteristics of gas jets are regarded as a key design factor because they have a direct influence on the amount of fuel supply into the cylinder and on the mixture formation around the nozzle exit of the gas injector. The experiments for investigating the characteristics of shockwaves, however, are very expensive and time-consuming. Therefore, a three-dimensional numerical model was developed in this study to examine the characteristics of shockwave structures and the change in the shock of the underexpanded gas jet for various injection conditions, using DES(detached eddy simulation) based on the Eulerian approach. In addition, the analysis results were verified by comparing the penetration length with the test results of the previous studies [10]. The obtained computation result is in good agreement with the experimental value, with a less than 5 % difference. It can be found that the normal pattern of repeated barrel shockwaves, the regular reflection pattern with reflection shock added, and the Mach disk pattern with Mach disk shock, are successively generated as the NPR increases. Additionally, this study investigated the effect of geometrical modification on the shock structure by comparing two different geometries: a flattened nozzle exit and an inner-stepped nozzle exit. For the results, Mach disks started to emerge over an NPR of 3.37 in the case of the flattened nozzle exit. On the other hand, in the case of the inner-stepped nozzle exit, Mach disks began to occur when the NPR was over 6. The study results show that the inner-stepped nozzle exit has a much stronger Mach disk inhibition effect, resulting in good mixture formation even at higher NPR conditions compared with the flattened nozzle exit. |
| 원문(PDF) | 다운로드 Journal Site |