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Modern commercial dual fuel engines operating in gas mode has the same level of fuel efficiency as the diesel mode. The NOx emissions level is reduced ten fold and satisfies the most stringent European 1/2 TA-Luft regulation. THC emissions can be controlled by the oxidation-catalytic process. High efficiency low NOx emissions gas engine performance is achieved by the following: Same power cylinder components as the basic diesel. Retarded timing together with short heat release duration by using Micropilot/Microcup designs. Lean lambda of 2.0 to 2.2. Minimal pilot fuel, 1% or less. Centrally located ignition if practical. Low air charge temperature at high load for high BMEP. 20-30% lower lambda at part load (compared to full load) achieved by compressed air bypass, skipfire, or variable geometry turbo. This paper provides only a qualitative treatise on gas engine combustion and the effects of fuel quality and engine design on combustion. Additional research is warranted.

This paper describes an integrated approach to the reduction of three pollutants; HC, CO, and NOx, as well as the soluble organic fraction of particulate matter emitted from engines operating with excess air. This technology is applicable to all lean burn engines and is particularly pertinent to natural gas, methane, and propane fueled engines due to the difficulty of catalytic oxidation of low molecular weight hydrocarbons, such as methane. The technology uses existing catalytic materials and combines a novel approach to thermal management of the catalyst bed. Additionally, a HC rich exhaust serves as a reducing agent for a deNOx catalyst as well as a source of chemical energy to heat the catalyst. This paper will detail the configuration of the catalyst system during testing, the test conditions under which the unit was run, and the results of emissions reduction and mechanical integrity tests.

Emissions from trucks and buses equipped with Caterpillar dual-fuel natural gas (DFNG) engines were measured at two chassis dynamometer facilities: the West Virginia University (WVU) Transportable Emissions Laboratory and the Los Angeles Metropolitan Transportation Authority (LA MTA). Emissions were measured over four different driving cycles. The average emissions from the trucks and buses using DFNG engines operating in dual-fuel mode showed the same trends in all tests - reduced oxides of nitrogen (NOx) and particulate matter (PM) emissions and increased hydrocarbon and carbon monoxide (CO) emissions - when compared to similar diesel trucks and buses. The extent of NOx reduction was dependent on the type of test cycle used.

Natural gas is a low cost, abundant and clean burning fuel. Current internal combustion engines can be readily adapted to use natural gas fuel either in conjunction with conventional liquid fuels or as dedicated systems. Use of modern electronic controls allows consideration of new engine management strategies that are not practical or even possible with mechanical systems. The preferred approach is pre-mixed lean burn with cylinder-by-cylinder fuel injection and full time control of optimized air/fuel ratio and ignition.

Dual-fuel pilot ignited natural gas engines have several intrinsic advantages relative to spark ignited; mainly higher thermal efficiency and lower conversion costs. The major drawback is associated with light loads. This paper discusses objectives, approaches, methods and results of the development of strategies which overcome the drawbacks and enhance the advantages. Development of a pilot fuel injection system, having a delivery of only 1 mm3 at a duration of 0.6 ms, was described in a previous paper. This paper concentrates on the results of strategies to reduce unburned methane in the exhaust and to increase the substitution of gas at light loads through skip-fire, by-passing boost air and exhaust gas recirculation techniques. Engine tests proved that with these strategies, diesel fuel replacement of more than 95% over the entire engine operating map, including idle, can be achieved and current and anticipated future emission standards satisfied.

The paper discusses objectives, approaches and results of the development of a pilot fuel injection system (FIS) for a dedicated, compression ignition, high-speed, heavy duty natural gas/diesel engine. The performance of the pilot FIS is crucial for the success of a dual fuel concept. The Servojet electro-hydraulic, accumulator type fuel system was chosen for the pilot fuel injection. An alternative pilot FIS based on the “water hammer” (WH) effect was also considered. The modifications to a stock 17 min injector is described. Three different types of pilot injector nozzle were investigated: standard Valve Covered Orifice (VCO), modified minisac and new designed, unthrottled pintle. Preliminary results from engine tests proved that the optimum pilot fuel quantity is the minimum quantity. Based on that finding, the pilot FIS design was further optimized.

Research on the Catalytic Plasma Torch (CPT) ignition system was conducted this last year at BKM, Inc. in San Diego. The results showed that under certain conditions CPT can not only time ignition properly, but also extend the lean stability limit. This concept is based upon compression ignition of the charge in the CPT's integral pre-chamber. Compression ignition is induced by timed catalytic reduction of the pre-chamber's activation energy. This produces almost instantaneous combustion in the pre-chamber and is divided into multiple high velocity torches to rapidly ignite the main chamber charge. The timing of the ignition event is based on the location of the heated catalyst in the pre-chamber and the mass of the charge inducted into the cylinder. The base timing curve can be modified via current control which effects the catalyst activity. Dynamic modification of the timing event is accomplished by using the catalyst as an in-cylinder hot wire anemometer.

Increasing emphasis on natural gas as a clean, economical, and abundant fuel, encourages the search for the optimum approach to management of fuel, air and combustion to achieve the best results in power, fuel economy and low exhaust emissions. Electronic injection of fuel directly into the throttle body, intake ports or directly into the cylinder offers important advantages over carburetion or mixing valves. This is particularly true in the case of installations in which the gas supply is available at several atmospheres pressure above maximum intake manifold pressure. The use of choked-flow pulse- width-modulated electronic injectors offers precision control over the engine operating range with a wide variety of options for both stoichiometric and lean bum applications. A complete system utilizing commercially available components together with the application, calibration and engine mapping techniques is described.

In the quest for cleaner air, there are numerous approaches in various stages of study, development and implementation. Despite stringent clean air regulations, which have reduced previously uncontrolled engine exhaust emissions by more than 10 fold, the population of pollution sources is growing faster than the reduction in the pollution rate per source. Various alternatives include cleaner fuels and alternative fuels, cleaner engines and alternative engines, as well as bold proposals such as electrical power or hydrogen as a fuel, which offer some measure of improvement. However, most efforts to date appear to fall in the category of too little, too late or too costly. It is concluded that a major changeover to natural gas as an alternative fuel for use in most engines, with a program that includes retrofit of old engines and modification of new engines to utilize natural gas, offers an effective and rational solution.

Through the joint efforts of BKM, SPI, AFS and Belarus, an advanced, all- electronic dual fuel system has been developed for retrofit applications on the Belarus D-144, four-cylinder, 4.15 liter, 44.7 KW diesel engine. The system features all electronic control on both full diesel or up to 90 % gas with automatic and instant changeover capability. The existing mechanical diesel injection system was replaced with an all electronic, hydraulically actuated, diesel injection system coupled with timed multi-point electronic injection for the gas system. The control strategy does not utilize inlet throttling typically used on gas fueled engines. The effectiveness of this simplified control system is assumed to be the result of a degree of charge stratification. The D-144 engine is utilized in a wide variety of industrial, farm and highway applications. Special application requirements can be accommodated by programming the EPROM control chip.

This paper addresses both the generation of various injection rate shapes using the accumulator type electronic injector, and their effects on engine combustion and sound level performance as recorded by a 500,000 sample-per-second PC board Engine Analyzer. An advanced hydro-electronic unit injector has been developed by BKM to offer a wide range of readily adjustable injection rate shapes to match a particular engine combustion configuration. The system is adaptable to both fixed (passive) rate shaping and active on-line optimization with electronically adjustable injection timing, fuel quantity, and injection rate. The effects of a range of injection rate shapes on fuel economy, exhaust emission, heat release rate, and noise level are readily available and properly documented within a few minutes of the engine running.

An electronically-controlled, two-stage high pressure diesel unit injector is the focus of a study of injection characteristics. The fourteenth order nonlinear mathematical model of the injector is developed and a computer simulation written. The simulation is verified by good agreement between predicted and measured accumulator pressure histories and fuel deliveries for fuel and water tests over a range of rail pressure settings. Stroboscopic flash photographic and dynamic laser attenuation measurements of spray penetration distance and spray cone angle are obtained for the injector operating at peak injection pressures of 80, 110 and 145 MPa. The experiments are performed with water injection into quiescent air at laboratory conditions. At the highest value of peak injection pressure of 145 MPa, the penetration length history exhibits a slope of approximately 250 m/s with a corresponding spray cone angle of 16°.

Additional data has been analyzed on the effect of engine size on thermal efficiency. The comparison has been expanded to show the trends separately for engines developed by several different manufacturers. The data confirm the conclusion that engines below 2.0 liters per cylinder seem to deteriorate in fuel economy faster than would have been predicted from the behavior of larger engines. It is postulated that such deterioration results from a combination of less than optimum fuel spray, wall wetting, and perhaps a greater heat transfer loss than was anticipated. The paper focuses on engines in the size range under two liters per cylinder and addresses some of the problems to be resolved. Means for generating and controlling fuel spray and injection rate shape are presented along with experimental data on fuel sprays and engine combustion.

The effect of high pressure injection (using an accumulator type unit injector with peak injection pressure of approximately 20,000 psi, having a decreasing injection rate profile) on combustion was studied. Combustion results were obtained using a DDA Series 3–53 diesel engine with both conventional analysis techniques and high speed photography. Diesel No. 2 fuel and a low viscosity - high volatility fuel, similar to gasoline were used in the study. Results were compared against baseline data obtained with standard injectors. Some of the characteristics of high pressure injection used with Diesel No. 2 fuel include: substantially improved ignition, shorter ignition delay, and higher pressure rise. Under heavy load - high speed conditions, greater smokemeter readings were achieved with the high pressure injection system with Diesel No. 2 fuel. Higher flame speeds and hence, greater resistance to knock were observed with the high volatility low cetane fuel.

Review of the theories, observations, and trends presented in Part I of this set of papers leads to the projection of certain aspects of injection sprays, mixture preparation, and combustion which may be designed to enhance diesel engine efficiency and reduce unwanted emissions. The basic concept is that control of the size, distribution and time of introduction of fuel droplets will result in a predictable optimized combustion event. Burning rate is controlled by droplet size and not by injection rate. The results of the ideal combustion and mixture preparation models are compared with experimental data and show good correlation. The preference for high-pressure, short-duration, non-wall-wetting and uniformly distributed fuel sprays coupled with controlled fast diffusion burning is clearly evident. With high injection rates, it may be desirable to trade swirl rate for additional combustion air.

A new method for direct cylinder injection for two-stroke cycle engines is described. The technique utilizes simple hole type nozzles, accumulator injectors, medium pressure (100 bar), pressure metering, and full electronic controls. The objectives of the system are to accomplish, in a single injection, the four essentials of effective fuel injection (a) metered quantity of fuel, (b) desired spatial distribution, (c) timing of injection, (d) complete vaporization prior to the start of combustion. Special techniques such as “cloud-stratified charge” and “skip-fire” are discussed as well as the special design features of the components and control systems. Data presented include details of spray formation and engine performance with dramatic reduction in fuel consumption and exhaust emissions.

A new type of diesel fuel injection uses a simple, medium-pressure, common-rail system with pressure intensifier and accumulator type unit injectors with digital electronic control to achieve high performance at low cost. The desirable features of high injection pressures with quantity and timing controlled directly by microprocessor are attained with a simple unique system. Data are presented on performance, efficiency, emissions, and relative cost. It is concluded that electronically controlled high pressure injection offers a practical and economical solution for efficient combustion in a diesel engine.

A new type of diesel fuel injection uses a simple, medium-pressure, common-rail system with pressure intensifier and accumulator type unit injectors with direct electronic control to achieve high performance at low cost. The desirable features of high injection pressures with quantity and timing controlled directly by microprocessor are attained with a simple unique system. Data are presented on performance, efficiency, emissions, and relative cost. It is concluded that electronically controlled high pressure injection offers a practical and economical solution for efficient combustion in diesel engines.