Experimental investigation of partially premixed combustion in a DISI natural gas engine: Performance, Combustion behaviour, and Crevice hydrocarbons
Bibliographic record
Abstract
The use of partially premixed combustion (PPC) can overcome current limitations of natural gas (NG) fuelled engines. Experimental results are presented for NG PPC in a spark ignited single cylinder research engine. Injection timing of directly injected NG was varied from the beginning of the compression stroke to just before top dead centre (BTDC). Decreasing time available for mixing before ignition resulted in increasingly stratified mixtures as injection approached TDC. The study’s goals were: To explore the stable operating range for a flat plane NG injector and for a cone pattern injector with a 100 degree included angle, to demonstrate the impact of injection timing on piston top land crevice emissions for the two injector nozzles through analysis of cycle-by-cycle exhaust port hydrocarbon (HC) measurements, and to highlight the effect of NG injection timing on fuel supply pressure requirements. Injected fuel residence time between the end of injection and ignition had a critical influence on combustion behaviour for both nozzles. The cone nozzle confined fuel to the piston bowl at earlier injection timings, reducing crevice penetration and expanding the feasible operating range. Optimal operation was achieved with the cone nozzle at 33–34 crank angle degrees (CAD) residence time, corresponding to 66 and 73 CAD BTDC injection timings for 34 and 69 kPa gauge intake pressures respectively. At the optimal operating point, indicated mean effective pressure (IMEP) increased 21.0 and 39.5% and HC from crevice outgassing decreased by 76.4 and 60.9% for the two intake pressures respectively relative to premixed operation. • Natural gas was direct injected during the compression stroke and spark ignited. • Later injection created fuel stratification, increasing IMEP and combustion stability. • Cycle resolved exhaust port hydrocarbons measured by fast flame ionization detector. • Later injection demonstrated large reduction in crevice HC emissions. • Smaller included angle improved performance and fuel utilization at earlier SOI.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".