Current diesel technologies involve a broad spectrum of combustion regimes. Previous diesel combustion models either lack the universality across various combustion regimes or suffer computational cost. This dissertation discusses the development of a phenomenological framework to identify and understand key in-cylinder processes that influence the overall performance of a compression ignition engine. The first part of this research is focused on understanding the ignition delay (ID) of diesel fuel in a pilot-ignited partially premixed, low temperature natural gas (NG) combustion engine. Lean premixed low temperature NG combustion is achieved by using small pilot diesel sprays (2-3% of total fuel energy) injected during early compression stroke (about 60° BTDC). Modeling ignition delay at advanced pilot injection timings (50°-60°BTDC) presents unique challenges. In this study, single component droplet evaporation model in conjunction with the Shell hydrocarbon autoignition (SAI) model is used to obtain ignition delay predictions of pilot diesel over a wide range of injection timings (20°-60° BTDC). Detailed sensitivity analysis of several SAI model parameters revealed that the model parameter Aq, which influences chain initiation reactions, was most important to predict ignition delays at very lean equivalence ratios. Additional studies performed to ascertain critical model parameters revealed that ignition delay was particularly sensitive to intake manifold temperature over the range of injection timings investigated. Finally, the validated SAI model was used to predict ignition delays of pilot diesel fuel at various exhaust gas recirculation (EGR) substitutions, intake manifold temperatures and engine loads (bmep = 6 bar and 3 bar, respectively). The second part of this research involved the development of a phenomenological simulation of diesel/biodiesel combustion, which included sub-models for diesel spray entrainment, evaporation, ignition and premixed and mixing-controlled combustion. In the simulation, the cylinder contents consisted of an unburned zone, packet zones, and a burned zone. The simulation, after appropriate calibration, was capable of predicting cylinder pressure and heat release rates at different engine load conditions over the injection timing range of 0°BTDC to 10°BTDC. The total number of packets, droplet evaporation rates, air entrainment rates; ignition delay and premixed/mixing-controlled reaction rate parameters had a profound influence on combustion predictions.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-1224 |
| Date | 12 May 2012 |
| Creators | Jha, Saroj Kumar |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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