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Technical Paper


Technical Paper

Modeling NOx Emissions from Lean-Burn Natural Gas Engines

A zero-dimensional cycle simulation model coupled with a chemical equilibrium model and a two-zone combustion model has been extended to predict nitric oxide formation and emissions from spark-ignited, lean-burn natural gas engines. It is demonstrated that using the extended Zeldovich mechanism alone, the NOx emissions from an 8.1-liter, 6-cylinder, natural gas engine were significantly under predicted. However, by combining the predicted NOx formation from both the extended Zeldovich thermal NO and the Fenimore prompt NO mechanisms, the NOx emissions were predicted with fair accuracy over a range of engine powers and lean-burn equivalence ratios. The effect of injection timing on NOx emissions was under predicted. Humidity effects on NOx formation were slightly under predicted in another engine, a 6.8-liter, 6-cylinder, natural gas engine. Engine power was well predicted in both engines, which is a prerequisite to accurate NOx predictions.
Technical Paper


Technical Paper

Improved Atomization of Methanol for Low-Temperature Starting in Spark-Ignition Engines

Heating neat (100 percent) methanol fuel (M100) is shown to improve dramatically the atomization of the fuel from a production, automotive, port fuel injector of pintle design. This improvement is particularly noticeable and important when compared with atomization at low fuel temperatures, corresponding to those conditions where cold-start is a significant problem with neat methanol-fueled (M100) vehicles. The improved atomization is demonstrated with photographs and laser-diffraction measurements of the drop-size distributions. Fuel temperatures were varied from -34°C (-29°F to 117°C (243°F), while the boiling point of methanol is 64.7°C (148.5°F). Air temperatures were ambient at about 24°C (75°F). For temperatures above the boiling point, some flash boiling and vaporization were presumably occurring, and these may have contributed to the atomization, but the trends for drop size did not shown any discontinuity near the boiling point.
Technical Paper

A PC-Based Model for Predicting NOx Reductions in Diesel Engines

A menu-driven, PC-based model, ALAMO_ENGINE, has been developed to predict the nitrogen oxides (NOx) reductions in direct-injected, diesel engines due to exhaust gas recirculation (EGR), emulsified fuels, manifold or in-cylinder water injection, fuel injection timing changes, humidity effects, and intake air temperature changes. The approach was to use a diesel engine cycle simulation with detailed gas composition calculations for the intake and exhaust gases (including EGR, water concentration, fuel-type effects, etc.), coupled with a code to calculate stoichiometric, adiabatic flame temperatures and expressions that correlate measured NOx emissions with the flame temperature. Execution times are less than 10 seconds on a 486-66 MHz PC.