Double injection strategy in a small-bore gasoline compression ignition engine

Download files
Access & Terms of Use
open access
Copyright: Goyal, Harsh
Altmetric
Abstract
Gasoline compression ignition (GCI) engines achieve higher engine efficiency and lower NOx/soot emissions than diesel compression ignition engines through partially premixed charge combustion. The thesis aims to evaluate double-injection strategies for GCI combustion, their effects on efficiency/emissions, and ignition process. Two engines were used: a single-cylinder metal engine for performance/emissions testing and an optical engine sharing the same geometry. From the performance/emissions tests, it was shown that the double-injection strategy implementing early near-BDC and late near-TDC injections shows higher efficiency and lower emissions than the single-injection strategy. The GCI combustion showed high sensitivity to advanced second injection timing with advanced combustion phasing leading to increased engine efficiency, reduced smoke/uHC/CO emissions but higher noise and NOx. For fixed combustion phasing, the increased first injection proportion causes lower peak heat release rate due to increased homogeneity of the first-injection charge and thereby achieving lower smoke/NOx/noise emissions but higher uHC/CO. Regarding ignition quality, higher octane fuel at fixed mixture homogeneity showed higher power output due to increased charge premixedness of the second-injection. Given the strong influence to mixture preparation and subsequent ignition processes, visualisation of combustion luminosity and OH* chemiluminescence was performed. The results show that single-injection leads to multiple auto-ignition kernel development from which isolated flame growth occurs while for double-injection, isolated flame growth is not clearly defined due to increased mixture homogeneity. Detailed measurements using PLIF imaging of fuel, HCHO, and OH showed that single-injection leads to low-temperature reaction from bowl-wall region due to extended ignition delay. The high-temperature reaction also starts from the bowl-wall region; however, this transition involves multiple ignition kernels that progressively merge to form large high-temperature reaction zones. In comparison, double-injection shows dispersed fuel distribution, higher HCHO consumption rate and faster OH development across all reaction zones, indicating faster low- to high-temperature reaction transition. These fundamental findings explain how double-injection-based GCI combustion generates less NOx/soot emissions than single-injection while achieving better combustion stability.
Persistent link to this record
Link to Publisher Version
Link to Open Access Version
Additional Link
Author(s)
Goyal, Harsh
Supervisor(s)
Kook, Sanghoon (Shawn)
Hawkes, Evatt
Creator(s)
Editor(s)
Translator(s)
Curator(s)
Designer(s)
Arranger(s)
Composer(s)
Recordist(s)
Conference Proceedings Editor(s)
Other Contributor(s)
Corporate/Industry Contributor(s)
Publication Year
2019
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
Files
download public version.pdf 7.51 MB Adobe Portable Document Format
Related dataset(s)