Christopher M. Atkinson

Factors Affecting Heavy-Duty Diesel Vehicle Emissions

Abstract Societal and governmental pressures to reduce diesel exhaust emissions are reflected in the existing and projected future heavy-duty certification standards of these emissions. Various factors affect the amount of emissions produced by a heterogeneous charge diesel engine in any given situation, but these are poorly quantified in the existing literature. The parameters that most heavily affect the emissions from compression ignition engine-powered vehicles include vehicle class and weight, driving cycle, vehicle vocation, fuel type, engine exhaust aftertreatment, vehicle age, and the terrain traveled. In addition, engine control effects (such as injection timing strategies) on measured emissions can be significant. Knowing the effect of each aspect of engine and vehicle operation on the emissions from diesel engines is useful in determining methods for reducing these emissions and in assessing the need for improvement in inventory models. The effects of each of these aspects have been quantified in this paper to provide an estimate of the impact each one has on the emissions of diesel engines.

Development of a linear alternator-engine for hybrid electric vehicle applications

This paper examines the design and operation of a generation system that utilizes a linear crankless internal combustion engine in conjunction with a linear alternator. This system directly utilizes the linear motion of the piston to drive the alternator rather than first converting to rotary motion. The result is a more compact, reliable, and efficient unit as the system has only one moving part, making the system ideal for use in series hybrid electric vehicles. This paper describes the overall system design as well as the subsystems including the engine and alternator. A dynamic simulation is then presented which utilizes the model developed to determine the output characteristics of the system. The prototype system was successfully tested, and experimental results are also included.

Numerical Simulation of a Two-Stroke Linear Engine-Alternator Combination

Series hybrid electric vehicles (HEVs) require powerplants that can generate electrical energy without specifically requiring rotary input shaft motion. A small-bore working prototype of a two-stroke spark ignited linear engine-alternator combination has been designed, constructed and tested and has been found to produce as much as 316W of electrical energy. This engine consists of two opposed pistons (of 36 mm diameter) linked by a connecting rod with a permanent magnet alternator arranged on the reciprocating shaft. This paper presents the numerical modeling of the operation of the linear engine. The piston motion of the linear engine is not mechanically defined: it rather results from the balance of the in-cylinder pressures, inertia, friction, and the load applied to the shaft by the alternator, along with history effects from the previous cycle. The engine computational model combines dynamic and thermodynamic analyses. The dynamic analysis performed consists of an evaluation of the frictional forces and the load (in this case the alternator load) across the full operating cycle of the engine. The thermodynamic analysis consists of an evaluation of each process that characterizes the engine cycle, including scavenging, compression, combustion and expansion, based on the first law of thermodynamics. Since the modeled engine was crankshaftless, a time-based Wiebe function (as opposed to a conventional crank angle-based approach) was used to express the mass fraction burned for the combustion process, while the combustion model used was a single-zone model. To render the model useful, the parameters used were based on experimental data obtained from the working example, including instantaneous shaft position, velocity and in-cylinder pressure. Also, a parametric study was performed to predict the behavior of the engine over a wide operating range, given variations in fuel combustion properties, the reciprocating mass of the piston shaft assembly, frictional load and the externally applied electrical load. INTRODUCTION AND LITERATURE REVIEW Free-piston engines have been a subject of research and development for several decades. A recent review of freepiston engine concepts has been conducted by Achten [16]. Free-piston engines utilizing internal combustion (as opposed to the external combustion Stirling engine, which suffers from poor power density) have their origin in the 1920’s when R. Pescara [1] patented their use as air compressors. Junkers in Germany developed a freepiston engine for use in German submarines in World War II. The French SIGMA free-piston gasifier saw service for decades in stationary power generation. The use of free-piston engines in automotive application was most heavily promoted in the period 1952 to 1961, when both General Motors and Ford Motor Company produced running prototypes [2], [3]. In both cases these engines were two-stroke, opposed piston spark ignited engines with combustion bounce/compression chambers. These engines where used as gasifiers to generate hot gases to drive exhaust turbines through which energy would be extracted. Development efforts largely ceased by the 1960’s as turbine powered vehicles were increasingly viewed as not commercially viable. The elimination of the crankshaft mechanism in free-piston engines provides potential for reduction in mechanical losses. Due to the fact that the piston is not constrained in a free-piston engine, the piston motion is not prescribed, and it varies from one operating regime to another. Characteristic of the free-piston engines is the fact that they do not have a flywheel. As a result, they do not accumulate energy from the previous cycles for the subsequent cycles, except in terms of achieving a greater or lesser stroke associated with greater or lesser gas compression energy. A linear engine operates somewhat similarly to a free-piston engine, the only difference being that the reciprocating assembly consists of two pistons connected by a common connecting rod, with each piston operating in its own cylinder.

Field Measurements of Particulate Matter Emissions, Carbon Monoxide, and Exhaust Opacity from Heavy-Duty Diesel Vehicles

Diesel particulate matter (PM) is a significant contributor to ambient air PM10 and PM2.5 particulate levels. In addition, recent literature argues that submicron diesel PM is a pulmonary health hazard. There is difficulty in attributing PM emissions to specific operating modes of a diesel engine, although it is acknowledged that PM production rises dramatically with load and that high PM emissions occur during rapid load increases on turbocharged engines. Snap-acceleration tests generally identify PM associated with rapid transient operating conditions, but not with high load. To quantify the origin of PM during transient engine operation, continuous opacity measurements have been made using a Wager 650CP full flow exhaust opacity meter. Opacity measurements were taken while the vehicles were operated over transient driving cycles on a chassis dynamometer using the West Virginia University (WVU) Transportable Heavy Duty Vehicle Emissions Testing Laboratories. Data were gathered from Detroit Diesel, Cummins, Caterpillar, and Navistar heavy-duty (HD) diesel engines. Driving cycles used were the Central Business District (CBD) cycle, the WVU 5-Peak Truck cycle, the WVU 5-Mile route, and the New York City Bus (NYCB) cycle. Continuous opacity measurements, integrated over the entire driving cycle, were compared to total integrated PM mass. In addition, the truck was subjected to repeat snap-acceleration tests, and PM was collected for a composite of these snap-acceleration tests. Additional data were obtained from a fleet of 1996 New Flyer buses in Flint, MI, equipped with electronically controlled Detroit Diesel Series 50 engines. Again, continuous opacity, regulated gaseous emissions, and PM were measured. The relationship between continuous carbon monoxide (CO) emissions and continuous opacity was noted. In identifying the level of PM emissions in transient diesel engine operation, it is suggested that CO emissions may prove to be a useful indicator and may be used to apportion total PM on a continuous basis over a transient cycle. The projected continuous PM data will prove valuable in future mobile source inventory prediction.

Development of a heavy-duty chassis dynamometer driving route

Abstract There is presently a lack of realistic driving cycles or schedules for the chassis dynamometer emissions testing of heavy-duty trucks. This research effort was motivated by the need for representative emissions measurement techniques to compare alternatively fuelled trucks with their diesel or gasoline counterparts operating in heavy-duty truck applications. Speed versus time and video recording data gathered from trucks in local delivery use were used to develop a city/suburban heavy vehicle route (referred to as the CSHVR) for Class 7 (11 794-14969 kg gross vehicle weight) and Class 8 (14969-36287 kg) delivery trucks. Statistical data were gathered on actual truck driving behaviour, as well as 60 h of actual speed versus time driving information. A cycle was then developed by joining microtrips from the actual truck operation and verifying that it was representative of the whole database. A driving route was derived from this cycle with the help of the video data, and with the vehicle deceleration rates modified for practical reasons. It was found that a more powerful truck could bias its exhaust gas emissions by not aggressively applying full power while following a conventional speed versus time trace cycle. In comparison with a speed versus time cycle, a route allows sections of free acceleration (at full power) until a desired overall operating distance is met. A route is defined by a path that a truck must follow where driving instructions are dependent upon the acceleration of the truck, road conditions and speed limitations. The new route has been successfully employed in the emissions testing of several Class 8 tractors and was found to yield emission rates (in g/mile) that were higher than those for the previously documented WVU five-mile route (8 km in length) in the case of a Ford 36287 kg (80000 lb) GVWR tractor with a mechanically injected Cummins 261 kW (350 hp) engine.

Amplitude reduction and phase lag in fluidized-bed pressure measurements

Abstract Dual statitic pressure probes (DSPPs) provide detailed information on fluidized-bed hydrodynamics. However, the geometry of the DSPP and the type of transducer across which the probe stems are connected have a profound influence on the measured differential pressure. Analysis shows that it is important to choose a transducer with low dead volumes and even more important to ascertain that the dead volumes associated with each transducer tapping are equal. Partial blockage of one of the tubes will also precipitate erroneous data collection. Experimental results support the analysis.

Gas sampling from fluidized beds: A novel probe system

Abstract A system to sample gas from bubbles in a fluidized bed was designed, built and tested. It consisted of a dual-stem static-pressure probe (DSPP) to detect a rising bubble and a gas-sampling probe situated a small distance above the DSPP, together with a computer and hardware to interface the two probes. The DSPP was shown to provide reliable information on rising bubbles so that sampling criteria could be implemented. Tests in a gas—liquid column and in a small fluidized bed confirmed satisfactory gas sampling. The system can be adapted to operate in hot beds and is viewed as an important research tool and as a future process control device.

Correlating local tube surface heat transfer with bubble presence in a fluidized bed

Abstract A fifty-one millimeter outside diameter heat transfer tube of thirteen millimeter wall thickness was fitted horizontally into a cold bubbling bed of sand and fed with a supply of hot water. The surface of the tube was instrumented with five miniature thermocouples and, in addition, two pressure taps were drilled into the tube to infer bubble presence from vertical pressure gradients. The relationships between bubbling frequency and bed height as well as bubbling frequency and fluidizing velocity are reported. The correlation between transient temperature and differential pressure data shows the influence of bubble events on the local tube heat transfer. Velocity of a bubble at the tube surface could also be inferred from multiple thermocouple data.

On-Road Use of Fischer-Tropsch Diesel Blends

Alternative compression ignition engine fuels are of interest both to reduce emissions and to reduce U.S. petroleum fuel demand. A Malaysian Fischer-Tropsch gas-to-liquid fuel was compared with California No.2 diesel by characterizing emissions from over the road Class 8 tractors with Caterpillar 3176 engines, using a chassis dynamometer and full scale dilution tunnel. The 5-Mile route was employed as the test schedule, with a test weight of 42,000 lb. Levels of oxides of nitrogen (NO{sub x}) were reduced by an average of 12% and particulate matter (PM) by 25% for the Fischer-Tropsch fuel over the California diesel fuel. Another distillate fuel produced catalytically from Fischer-Tropsch products originally derived from natural gas by Mossgas was also compared with 49-state No.2 diesel by characterizing emissions from Detroit Diesel 6V-92 powered transit buses, three of them equipped with catalytic converters and rebuilt engines, and three without. The CBD cycle was employed as the test schedule, with a test weight of 33,050 lb. For those buses with catalytic converters and rebuilt engines, NO x was reduced by 8% and PM was reduced by 31% on average, while for those buses without, NO x was reduced by 5% and PM was reduced by 20% on average. It is concluded that advanced compression ignition fuels from non-petroleum sources can offer environmental advantages in typical line haul and city transit applications.

Turbocharging a bi-fuel engine for performance equivalent to gasoline

A bi-fuel engine capable of operating either on compressed natural gas (CNG) or gasoline is being developed for the transition to alternate fuel usage. A Saturn 1.9 liter 4-cylinder engine was selected as a base powerplant. A turbocharger was installed to increase the density of the intake charge and thereby regain the volumetric efficiency lost with CNG. Reductions from baseline in hydrocarbon and carbon dioxide emissions were achieved at power levels equivalent to and slightly higher than the baseline. Brake thermal efficiency values were not significantly different in any case. 8 refs., 12 figs.