Gasoline compression ignition (GCI) is a promising powertrain solution to address the increasingly stringent regulation of oxides of nitrogen (NOx) and a new focus on greenhouse gases. This work was conducted in a Cummins ISX15 heavy-duty diesel engine. The test fuel was an ethanol-free gasoline with a research octane number (RON) of 93.  In the experimental investigation, the engine geometric compression ratio (GCR) was varied from 15.7 to 18.9.

Over a load range of 5 to 15 bar BMEP, GCI is shown to produce diesel-like fuel efficiency at an enhanced NOx-soot tradeoff by implementing a split injection strategy and a two-stage combustion process. GCI’s NOx-soot tradeoff benefit was found to be stronger at lower CR and lighter load as gasoline’s lower reactivity becomes more impactful. Overall, the test results suggest that a GCR of 16-17 may be favored at an engine-out NOx level of 1-1.5 g/kWh.  In addition, at 17.3 GCR, the benefit of the split injection strategy was extended to warm and cold idle conditions, leading to improved combustion stability and lower hydrocarbon (HC) and carbon monoxide (CO) emissions.

To better utilize gasoline’s lower reactivity for medium-to-high load operation, the impact of both early and late intake valve closing (EIVC and LIVC) was studied at 17.3 GCR by performing closed-cycle, 3-D CFD combustion simulations coupled with 1-D engine cycle analysis. At medium to high load, variable valve actuation was shown to be an effective means to further improve the NOx-soot tradeoff by lowering the engine effective compression ratio (ECR) and lengthening the ignition delay.  Moreover, the fuel efficiency was improved by tailoring the fuel injection strategy at lower ECR and carefully adjusting the engine thermal boundary conditions.  


Impact of Geometric Compression Ratio and Variable Valve Actuation on Gasoline Compression Ignition in a Heavy-Duty Diesel Engine

Division / Sponsors: 
Internal Combustion Engine Division (ICED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2020/volume/84034

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