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A technology path has been identified for development of a high efficiency, durable, gasoline engine, targeted at achieving performance and emissions levels necessary to meet heavy-duty, on-road standards of the foreseeable future. Initial experimental and numerical results for the proposed technology concept are presented. This work summarizes internal research efforts conducted at Southwest Research Institute. An alternative combustion system has been numerically and experimentally examined. The engine utilizes gasoline as the fuel, with a combination of enabling technologies to provide high efficiency operation at ultra-low emissions levels. The concept is based upon very highly-dilute combustion of gasoline at high compression ratio and boost levels. Results from the experimental program have demonstrated engine-out NOx emissions of 0.06 g/hp/hr, at single-cylinder brake thermal efficiencies (BTE) above thirty-four percent.

Development of a natural gas-fueled engine capable of throttleless operation is discussed in this paper. This development was conducted under a program funded by the National Renewable Energy Laboratory to investigate methods to increase the efficiency of natural gas engines. In-cylinder fuel-air charge stratification was pursued as the mechanism for throttleless operation. Various methods of charge stratification were investigated, including direct injection, stratified charge (DISC) and a fuel injected prechamber (FIPC). The FIPC combustion system was found to be a more practical solution to the problem of charge stratification. Performance and emissions results from this engine configuration are presented and comparisons are made between current natural gas engines and the prototype FIPC engine.

The engine selected for this work was a Caterpillar 3176 engine. Engine exhaust emissions, performance, and heat release rates were measured as functions of engine configuration, engine speed and load. Two engine configurations were used, a standard 1994 design and a 1994 configuration with EGR designed to achieve a NOx emissions level of 2.5 gm/hp-hr. Measurements were performed at 7 different steady-state, speed-load conditions on thirteen different test fuels. The fuel matrix was statistically designed to independently examine the effects of the targeted fuel properties. Cetane number was varied from 40 to 55, using both natural cetane number and cetane percent improver additives. Aromatic content ranged from 10 to 30 percent in two different forms, one in which the aromatics were predominantly mono-aromatic species and the other, where a significant fraction of the aromatics were either di- or tri-aromatics.

An electromagnetic valve actuation (EVA) system was developed and applied to a Kohler Command Series engine. Engine development and testing was conducted for the purpose of evaluating the performance of the EVA-equipped engine, running on natural gas, in an engine-test laboratory environment. As part of this effort, a personal computer-based engine control system, which managed the fueling, ignition, throttling, and intake/exhaust valve control functions, was developed. The evaluation included an investigation into increasing engine power output and full load efficiency, as well as increased part load efficiency. Techniques including optimized valve events as a function of operating condition, and throttleless operation using early and late intake valve closing are presented. Engine simulation results are compared with actual engine data and presented in this paper.

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.

An experimental program to develop a practical natural gas-fueled locomotive engine was conducted. Six natural gas-fueled combustion systems for an EMD 710-type locomotive engine were developed and tested. The six systems were evaluated in terms of NOx and CO emissions, thermal efficiency, knock tolerance, and other practical considerations. Each combustion system was tested at Notch 5, 100-percent load, Notch 8, 80-percent load, and Notch 8, 100-percent load conditions. In general, all of the technologies produced significantly lower NOx emissions than the baseline diesel engine. Based on the results of the tests and other analyses, a late cycle, high-injection pressure (LaCHIP) combustion system, using a diesel pilot-ignited, late cycle injection of natural gas with a Diesel-type combustion process, was determined to provide the most practical combustion system for a natural gas-fueled, EMD 710-powered locomotive.

The effect of humidity on the lean misfire limit and emissions from a lean burn, natural gas engine is described in this paper, along with a description of a practical humidity compensation method for incorporation into an electronic control system. Experiments to determine the effects of humidity on the lean limit and emissions are described. Humidity increases were shown to decrease the rate of combustion, reduce NOx emissions, and increase the levels of unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. Data and calculations are also presented which demonstrate that increases in humidity will cause enleanment in a typical closed loop control system utilizing a universal exhaust gas oxygen (UEGO) sensor. A prototype system for humidity sensing and subsequent compensation based on these findings was implemented, and the system was found, through additional testing, to compensate for humidity very effectively.

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.

Development of a heavy-duty natural gas engine to improve its lean operating characteristics is detailed in this paper. Testing to determine the lean misfire limit is described, as well as investigations into the cause of lean misfire in this engine. Details of engine modifications to improve the lean misfire limit are also included. The development process resulted in a significant improvement in the lean performance of the engine (i.e., an extended lean misfire limit, better combustion stability, and lower hydrocarbon emissions).

Development of a state of the art, electronically controlled natural gas-fueled engine is detailed in this paper. The engine is a lean burn, turbochargedaftercooled engine controlled by a full authority electronic control system. This system controls fuel metering, spark timing, boost pressure, throttle position, and governing. The control system features closed-loop/adaptive-learn fuel control with feedback provided by a universal exhaust gas oxygen sensor. The development of the engine included development of the control system and other engine components, as well as a substantial amount of steady-state and transient control system calibration work. This effort led to a final engine calibration which provides good efficiency and transient response while meeting CARB ULEV emissions levels.

High-speed movie films, and laser-diffraction drop sizing were used to evaluate the structure, penetration rate, cone angle, and drop size distribution of diesel sprays in a constant volume pressure vessel. As further means of evaluating the data, comparisons are made between the film measurements, and calculations from a dense gas jet model. In addition to the high-speed film data that describes the overall structure of the spray as a function of time, a laser diffraction instrument was used to measure drop size distribution through a cross-section of the spray. In terms of the growth of the total spray volume (a rough measure of the amount of air entrained in the spray), spray impingement causes an initial delay, but generally the same overall growth rate as an equivalent unimpeded spray. Agreement between measurements and calculations is excellent for a diesel spray with a 0.15 mm D orifice and relatively high injection pressures.

The optical spark plug probe and ionization head gasket probe developed at Sandia Laboratories were applied to one cylinder of a production multicylinder automotive gasoline engine. The purpose of this application is to eventually study combustion phenomena leading to high emissions under cold start and cold idle conditions. As a first step in studying cold start combustion and emissions issues, diagnostic instrumentation was simultaneously applied to a production engine under steady state idle, road load and an intermediate load-speed condition. The preliminary application of such instrumentation is the subject of the present paper. The spark plug probe was redesigned for ease of use in production engines and to provide a more robust design. The two probes were geometrically oriented to obtain radial line-up between the optical windows and ionization probes. Data were taken simultaneously with both probes at the three load-speed conditions mentioned above.

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.