Search Results

The internal combustion engine and associated powertrain are likely to remain the mainstay of mobility over the next twenty years and to remain a significant portion of the portfolio of technologies employed over a much longer period of time. Efficient combustion of all fuels (petroleum based or alternative) requires copious amounts of air particularly with downsized engines. Turbocharging technology thus becomes an even more critical part of reducing both global warming gas and urban pollutant emissions from IC engines. Gasoline engine downsizing and turbocharging have been shown to improve fuel economy by ∼20% in production vehicles. In addition to data over a wide range of engines/vehicles, the results of a simple analysis done on vehicles/engines/drive cycles are presented to show the benefits of turbocharging and downsizing in a parametric variation of downsizing in combination with other technologies.

A “new” concept combining existing technologies of engine downsizing, electrically assisted turbocharging and light hybrid powertrain is proposed. Published analysis of hybrid technology and data of production hybrid vehicles are used to show that much of the benefit is derived from engine downsizing. Engine downsizing results in operation more often at wider open throttle with reduced pumping work and higher efficiency conditions. Results from vehicles using turbocharged, downsized engines are used to further corroborate this conclusion. Fuel shut off during coasting and vehicle stopping/idling also contributes positively to fuel economy improvement. In a “full hybrid” configuration, electric motor and battery energy is used to compensate for engine downsizing to get high torque at low speeds. Brake energy recovery is used to charge batteries.

The State of California considers greenhouse gases (GHGs) to be air pollutants and has directed the Air Resources Board to adopt cost effective regulations for GHG emissions from motor vehicles. The northeastern states and Canada through NESCCAF have worked closely with CARB and CO2 equivalent emission regulations have been proposed. The eventual status of these regulations may not be clear, but what is clear is that there is a need to develop cost effective technology to reduce GHG emissions. This paper presents such technology. Advances in turbocharging technology relevant to both gasoline and diesel engines are described. Turbocharging, as a technology has been around for 70 years, but just like the internal combustion engine itself, it is far from being mature. Conventional evolutionary development of turbocharging such as inertia reduction, aerodynamics and bearing improvements have been ongoing.

Data on several hundred family sedan production vehicles over a ten-year period are analyzed to compare turbocharged with non-turbocharged engines. It is shown that for the same power turbocharging enables gasoline engine downsizing by about 30%, improves fuel economy by 8-10% while improving torque and acceleration performance. Data with experimental turbocharged, downsized gasoline engines also shows that in the same vehicle, for the same power and performance, downsized turbocharged engines can give about 18% improvement in fuel economy. The paper discusses these data and analyzes the benefits of engine downsizing and turbocharging and the possible mechanisms of these effects. It is shown that the same basic small engine can be turbocharged using a wide range of turbocharger matching to cover a power range normally covered by 4-5 engine families of progressively increasing displacement. Thus additional benefits can be obtained by rationalizing the engine product lines.

Heavy-duty diesel engines face increasingly stringent emissions regulations. The trade-off between fuel economy and NOx emissions and between NOx and particulate emissions is becoming even more critical. In the light of these regulations and the trade-off among many variables, air handling and exhaust gas recirculation (EGR) systems become increasingly important. Three advanced turbocharging technologies - variable nozzle turbochargers, integral EGR pump and an ultra-high pressure ratio, long life compressor are described. In this paper an overview of the designs and their impact on fuel economy, low speed torque, emissions and durability is described. It is shown that significant improvements in all four variables are readily possible with the use of these advanced turbocharging technologies. It is shown that variable nozzle (VNT) turbocharging reduces smoke particularly at low speeds by a factor of 5, improves torque at low engine speeds and improves fuel economy by about 3%.

Heavy duty trucks account for about 50 percent of the NOx burden in urban areas and consume about 20 percent of the national transportation fuel in the United States. There is a continuing need to reduce emissions and fuel consumption. Much of the focus of current work is on engine development as a stand-alone subsystem. While this has yielded impressive gains so far, further improvement in emissions or engine efficiency is unlikely in a cost effective manner. Consequently, an integrated approach looking at the whole powertrain is required. A computer model of the heavy duty truck system was built and evaluated. The model includes both conventional and hybrid powertrains. It uses a series of interacting sub-models for the vehicle, transmission, engine, exhaust aftertreatment and braking energy recovery/storage devices. A specified driving cycle is used to calculate the power requirements at the wheels and energy flow and inefficiencies throughout the drivetrain.

Diesel engine optimization for low emissions and high efficiency involves the use of very high injection pressures. It was generally thought that increased injection pressures lead to improved fuel air mixing due to increased atomization in the fuel jet. Injection experiments in a high-pressure, high-temperature flow reactor indicated, however, that high injection pressures, in excess of 150 MPa, leads to greatly increased penetration rates and significant wall impingement. An endoscope system was used to obtain movies of combustion in a modern, 4-valve, heavy-duty diesel engine. Movies were obtained at different speeds, loads, injection pressures, and intake air pressures. The movies indicated that high injection pressure, coupled with high intake air density leads to very short ignition delay times, ignition close to the nozzle, and burning of the plumes as they traverse the combustion chamber.

The mandate of the President's Clean Car Initiative to produce a car engine that will more than double the mileage per gallon of fuel and simultaneously eliminate pollutant emissions poses an unprecedented challenge to automotive industry. It ought to be met, it is claimed, by radical improvements in the execution of the exothermic process of combustion. The conventional combustion process involves the mode of flame traversing the charge (FTC). In this process control over the exothermic process is, in effect, non-existent. The exothermic process should be executed instead by a microprocessor controlled fireball mode of combustion (FMC) - the epitome of direct injection stratified charge (DISC) engine, featuring late injection and stratified combustion using a pulsed combustion jet (PCJ) system.

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.

Low intake manifold temperature, well below ambient, has many applications in internal combustion engines. In diesel engines, it can reduce NOx to a level of 2.0 g/hp-hr or below, going beyond the 1994 heavy duty diesel engine emissions standards. In gasoline engines, it can allow high compression ratio, turbocharged operation without end gas knock. This will permit ready conversion of some heavy duty diesel engines to gasoline operation at increased power density and lower emissions. In natural gas engines, it will allow base diesel engine to be converted to stoichiometric natural gas operation without increasing thermal loads. A three way catalyst can then be used to reduce emissions.

Fundamental regeneration rate data of cellular ceramic particulate traps are presented. The data were obtained from systematic bench experiments using scaled traps and simulated engine conditions. The study was conducted over a wide range of parameters, covering scaled regeneration flow rates from subidle engine flow to full flow at rated engine conditions, trap inlet temperatures from 500 to 650°C, oxygen concentrations from 5 to 21%, and particulate accumulation levels in the trap from a pressure drop ratio (relative to the clean unit) of 2 to 60. The effect of each parameter on the maximum trap temperature and regeneration time is independently studied and described. Favorable regeneration conditions in terms of minimizing the energy requirements for regeneration and avoiding trap destruction are identified. Finally, it is illustrated that regeneration maps of this type can be applied to develop a control logic for an automatic regeneration system.

Particulate and sulfate emission characteristics of two catalyzed radial- flow wire-mesh particulate traps are presented. The traps were found to be ineffective for particulate reduction. The first trap was dynamometer tested for 25 consecutive EPA Heavy Duty Diesel Transient Cycles and 40 hours of steady state operation. During steady state testing, particulates were sampled from both the raw and diluted engine exhaust. The total particulate matter was chemically analyzed for sulfate, organic, moisture, and nonextractable fractions. The data indicate significant conversion of fuel sulfur to hygroscopic sulfuric acid. Although solid carbon fraction was reduced, total particulate mass increased. Sulfuric acid condensation presented operational and particulate sampling difficulties. Sampling from the raw exhaust with heated lines showed good sulfur balance between fuel and exhaust contents, but sulfate emission also exceeded the baseline for total particulate matter.

Some results of a systematic study of the effects of fuel and chamber gas properties on the transient evaporating spray mixing process are presented. The study uses an existing two-dimensional stochastic thick spray model. The results show that the combustion process in typical heavy duty, quiescent, DI diesel engines can be mixing limited rather than vaporization limited. In addition, the results show that the mixing process of a transient evaporating spray is characterized by the combined effects of fuel evaporation and its turbulent mixing with the surrounding air. In general, increasing the evaporation rate alone does not necessarily increase the fuel-air mixing rate. Furthermore, two dimensionless parameters have been used to quantify the relative effects of fuel and chamber gas properties on the transient spray evaporation process. Finally, through detailed comparisons between spray and gas jet results, the transient evaporating spray mixing process is better understood.

Some results of a systematic analysis of important sources of hydrocarbon emissions from a direct injection diesel engine are presented. The following sources are considered and investigated: (1) local over-mixing, (2) poor end of injection, (3) fuel emptying from sac volume. The analysis uses systematic engine experiments and an existing two-dimensional thick evaporating spray model to determine the contribution of various hydrocarbon sources to the total hydrocarbon emissions in the exhaust. The results show that at idle and light load conditions, local overmixing is the major source of hydrocarbon emissions. The amount of fuel over-mixed is directly controlled by mixing rate, ignition delay, and the lean limit of combustion. Mixing rate calculations show that the injection rate shape and nozzle geometry are more important than the physical properties of the fuel in determining the amount of fuel overmixed.

Fundamental aspects of performance and regeneration of a porous ceramic particulate trap are described. Dimensionless correlations are given for pressure drop vs. flow conditions for clean and loaded traps. An empirical relationship between estimated particulate deposits and a loading parameter that distinguishes pressure drop changes due to flow variations from particulate accumulation is presented. Results indicate that trapping efficiencies exceed 90% under most conditions and pressure drop doubles when particulate accumulation occupies only 5% of the available void volume. Regeneration was achieved primarily by throttling the engine intake air. For various combinations of initial loading level, trap inlet temperature and oxygen concentration, it was found that regeneration rate peaked after 45 seconds from initiation.

Diesel engine exhaust and blowby gases were sampled and analyzed for nitrosamines. Tenax-GC traps were used as collection media. Three different engines were sampled. Tenax-GC material used contained significant quanities of dimethyl nitrosamine as impurities. A cleaning procedure was developed to precondition the traps. No nitrosamines were detected in either exhaust or blowby down to levels of 90 pptr and 10 pptr respectively.

Some results of a systematic study on sources of unburned hydrocarbons from direct injection diesel engines are presented. The following possible sources are considered and investigated experimentally and/or analytically: local over-mixing, local under-mixing, bulk quenching, cyclic misfire, cyclic variation, and wall effects. The significance of each source under a variety of operating conditions including simulated deceleration, light loads, high loads, and simulated acceleration are discussed. The results show that the formation of unburned hydrocarbons is mainly controlled by transient fuel-air mixing and bulk quenching processes. The fraction of fuel appearing as unburned hydrocarbons in the exhaust is greatest at light loads and retarded conditions.

A semiempirical, mathematical model describing the formation of nitric oxide in direct-injection diesel engines is derived. The model is used in conjunction with injection and thermodynamic cycle simulation programs. This approach enables prediction of nitric oxide emissions from design dimensions and operating parameters only, without the use of experimental data. Predicted results are compared with experiments for typical naturally aspirated and turbocharged engines. The accuracy of prediction is very good except under light-load naturally aspirated conditions. The model is used in an extensive parametric study, together with experimental verification. The agreement between prediction and experiments is excellent, except under conditions of excessive smoke or of high swirl.