https://orcid.org/0000-0003-4075-0861
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ABSTRACT
With the increasing temperature and pressure in the cylinder of the diesel engine, the in-cylinder environment gradually exceeded the thermodynamic critical point of hydrocarbon fuel. Compared with subcritical spray, the phase transformation mechanism of supercritical spray is essentially changed. In this paper, the n-heptane fuel sprays in three conditions case 1 (T1 = 400 K P1 = 2 MPa), case 2 (T2 = 600 K P2 = 2 MPa), and case 3 (T3 = 800 K P3 = 6 MPa) were obtained by high-speed digital schlieren method on the test platform of a constant volume combustion bomb. The spray liquid phase, liquid–gas mixed layer, and mixture were divided, and the variation rules of the spray cone angle, the liquid phase length, maximum interface thickness, and liquid–gas mixed layer area were discussed. The results showed that the higher the ambient temperature and pressure, the more severe the fragmentation of the spray. Compared with the subcritical condition, the spray penetration distance in the supercritical condition tended to be flat faster. Compared with 400 K, 2 MPa condition, the spray cone angle was about 33° and 50% larger at 800 K, 6 MPa condition. The liquid core area at 800 K, 6 MPa condition was 60 cm2, reduced by 75% compared with 400 K, 2 MPa condition, resulting in better spray diffusion and mixing with atmospheric gas. The sensitivity analysis of ambient temperature and pressure on spray characteristic parameters shows that temperature has a greater impact on the interface mixing layer area (VIP = 1.23), and pressure has a greater on penetration distance and spray penetration rate (VIP = 1.23). When the environmental conditions exceed the thermodynamic critical point, the area of the liquid–gas mixed layer increases due to the transformation of spray from evaporation to diffusion and the phenomenon of interfacial layer enrichment. In summary, the supercritical condition promotes the mixing of spray and environment and has a positive effect on spray diffusion and atomization.
Nomenclature
| NOx | = | nitric oxide |
| PM | = | Particulate matter |
| LTC | = | low-temperature combustion mode |
| HCCI | = | homogeneous charge compression ignition mode |
| PCCI | = | premixed charge compression ignition mode |
| CO2 | = | carbon dioxide |
| SMD | = | Sauter mean diameter |
| OPLS-AA | = | optimized potentials for liquid simulations-all atomic |
| PLS | = | Partial Least Squares |
| LTD | = | Limited |
| ASOI | = | After the Start of Injection |
| OTSU | = | on maximum interclass threshold method |
| RGB | = | Red As Integer, Green As Integer, Blue As Integer |
| PCA | = | principal component analysis |
| VIP | = | variable importance in projection |
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Funding
Notes on contributors
Ruina Li
Dr. Ruina Li is an associate professor at the School of Automotive and Transportation Engineering at Jiangsu University.
Liang Zhang
Mr. Liang Zhang is a master’s student at the School of Automotive and Transportation Engineering, Jiangsu University.
Yang Song
Mr. Yang Song is a master’s student at the School of Automotive and Transportation Engineering, Jiangsu University.
Yikai Qian
Mr. Yikai Qian is a master’s student at the School of Automotive and Transportation Engineering, Jiangsu University.
Zhong Wang
Dr. Zhong Wang is a professor at the School of Automotive and Transportation Engineering at Jiangsu University.
Yiqiang Pei
Dr. Yiqiang Pei is an associate professor at the School of Mechanical Engineering at Tianjin University.