Experimental investigation of partially premixed combustion in a DISI natural gas engine: Emissions behaviour
Bibliographic record
Abstract
Experimental results of partially premixed combustion using direct injection of natural gas during the compression stroke in a spark ignited single cylinder research engine are presented. A constant overall 0.70 equivalence ratio was used, with 34 and 69 kPa gauge intake pressures. Two injector nozzle designs were employed, one with a flat injection plane and one with a narrower 100 degree injection cone. Injection timing was varied to change the degree of premixing, from fully premixed with injection near BDC, to stratified combustion with injection near TDC. The effects on engine-out emissions of NO, CO, unburnt hydrocarbons, and particulate matter were assessed, along with the combustion efficiency determined from exhaust gas composition. Later injection timings resulted in reduced time for mixing before ignition, concentrating the fuel mass and increasing the local equivalence ratios of combustion. Unburnt hydrocarbon levels decreased with later injection timings as the fuel concentrated and injection was directed into the piston bowl. NO increased as local equivalence ratios approached stoichiometric, before reducing at richer local equivalence ratios. Late injection timings resulted in order of magnitude increases in CO and particulate matter as the low mixing time resulted in combustion at high local equivalence ratios. Combustion efficiency reached a maximum at moderate degrees of premixing. The residence time of the fuel between the end of injection and ignition was found to be a critical metric in defining the resulting emissions. The cone nozzle confined the fuel to the piston bowl at earlier injection timings, resulting in lower unburnt hydrocarbon emissions. Operation at 66 CAD BTDC injection timing and 34 kPa gauge intake pressure (giving 34.2 CAD of residence time) with the cone nozzle was found to give the optimal emissions profile. Unburnt hydrocarbon emissions decreased by 73.8%, but CO levels increased by a factor of 7.5 from 1338 to 11 443 ppm compared to fully premixed operation with injection near BDC. NO levels were moderate at 612 ppm, and particulate matter emissions increased moderately to 5.6E+06 #/cm 3 , compared to the motored concentration of 3.1E+05 #/cm 3 . The combustion efficiency of 90.3% was moderate in comparison to other operating points. • Later injections during compression stroke gave higher spatial fuel concentration. • NO emissions increased with combustion locally near stoichiometric. • Hydrocarbon emissions fell with fuel concentration and lower crevice penetration. • Overly late injections resulted in high CO and particulate matter emissions. • Smaller included angle injector confined fuel more at earlier injection timings.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".