LABORATORY TECHNIQUE, METHODS AND EQUIPMENT

<div class="section abstract"><div class="htmlview paragraph">Today turbo-diesel powertrains offering low fuel consumption and good low-end torque comprise a significant fraction of the light-duty vehicle market in Europe. Global CO₂ regulation and customer fuel prices are expected to continue providing pressure for powertrain fuel efficiency. However, regulated emissions for NO</div><div class="htmlview paragraph"> and particulate matter have the potential to further expand the incremental cost of diesel powertrain applications. Vehicle segments with the most cost sensitivity like compacts under 1400 kg weight look for alternatives to meet the CO₂ challenge but maintain an attractive customer offering. In this paper the concepts of downsizing and downspeeding gasoline engines are explored while meeting performance needs through increased BMEP to maintain good driveability and vehicle launch dynamics. A critical enabler for the solution is adoption of gasoline direct injection (GDi) fuel systems. GDi provides the ability to utilize increased scavenging without sacrificing hydrocarbon emissions because fueling and air controls can be separated. In-cylinder injection with GDi also provides charge cooling benefit yielding the knock reduction necessary for turbocharged applications. Several options within GDi are explored including multi-hole and single pintle spray generators, as well as side-mount versus central-mount applications. Both 3-cylinder and 4-cylinder base engine configurations are explored for turbocharged engines downsized to 1.2 L. Improvements in hydrocarbon emissions, heat losses and scavenging favor fewer cylinders. This is re-enforced by packaging and cost considerations. The next system aspect considered is emissions aftertreatment. Stoichiometric turbocharged GDi provides the lowest cost using the established 3-way catalyst. Stratified GDi is expected to require a lean NO</div><div class="htmlview paragraph"> trap (LNT) and diesel Euro 6 systems require addition of a diesel particulate filter (DPF) and possibly NO</div><div class="htmlview paragraph"> aftertreatment. Although the aftertreatment system to meet Euro 6 NO</div><div class="htmlview paragraph"> requirement is not known today, addition of a DPF, DPF with LNT, or DPF with urea selective catalytic reduction (SCR) represent significant cost and packaging challenges. The analysis concludes by comparing the 3-cylinder turbocharged GDi to other offerings in the context of value tradeoff of CO₂ reduction to system on-cost. Stratified 3-cylinder turbocharged GDi systems offer up to 22% CO₂ reduction compared to a baseline port-fuel-injected 4-cylinder engine. CO₂ reduction of 18% is possible for a stoichiometric GDi mechanization that employs variable valve actuation (VVA) and a conventional 3-way catalytic converter. At Euro 6 emission levels, stoichiometric 3-cylinder turbocharged GDi powertrains offer excellent value. The 3-cylinder turbo-diesel offers similar value if it is capable of meeting the NO</div><div class="htmlview paragraph"> emissions standard without lean aftertreatment. Powertrains with higher engine-out NO</div><div class="htmlview paragraph"> levels that require lean aftertreatment are significantly disadvantaged. Based on the price sensitivity of the compact car segment, the value analysis predicts the 3-cylinder turbocharged GDi engine as the powertrain of choice.</div></div>

<div class="htmlview paragraph">The effects of engine operating conditions on the octane requirement and the resulting knock-limited output were studied on a single cylinder engine using production cylinder heads. A 4-valve cylinder head with port deactivation was used to study the effect of fuel octane, inlet air temperature, coolant temperature, air/fuel ratio, compression ratio and exhaust back pressure. The effect of the thermal environment was studied in more detail using separate cooling systems for the cylinder head and engine block on a 2-valve cylinder head.</div> <div class="htmlview paragraph">The results of this study compared closely with results found in the literature even though the engine and/or operating conditions were quite different in many cases. Guidelines on the effect of various parameters on the octane requirement of an engine can be summarized as follows:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">Spark Advance: 1 ON/1° SA</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Air Temperature: 1 ON/7 K</div></li> <li class="list-item"><div class="htmlview paragraph">Air/Fuel Ratio: peaks at 5% rich of stoichiometric, decreases by around 2 ON / air/fule ratio around peak</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Pressure: 3-4 ON/10 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Compression Ratio: 5 ON/CR</div></li> <li class="list-item"><div class="htmlview paragraph">Exhaust Back Pressure: 1 ON/30 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Coolant Temperature: 1 ON/10 K (Similar effect of head and block temperature., Larger effect at low speed.)</div></li> </ul> </div>

<div class="section abstract"><div class="htmlview paragraph">In Automobile AC system, HVAC is one of major component as it controls the air flow and air distribution based on cabin requirement. HVAC kinematics mechanism is used for controlling the air flow based on passenger requirement inside the cabin. The air flow movement inside HVAC has a severe impact on servo motor/cable torque which is controlling the mechanism.</div><div class="htmlview paragraph">Simulation driven design method is widely used in world due to highly competitive automotive industry. Launching the product at the market within short span of time, with good quality and less cost is more challenging. Hence CAE/MBD based approach is more significant as it will reduce number of prototypes as well as the cost of testing.</div><div class="htmlview paragraph">The objective of the analysis is to predict the HVAC servomotor torque required to operate the HAVC linkages under operating conditions. The air pressure load will have significant impact on damper face which will cause torque at CAM as well as servo lever center. The torque values at servo lever center of HVAC kinematic mechanism with and without air flow is measured. This data is compared with actual test results. Hyper mesh is used for the meshing of the model. Motion view is used for the kinematic analysis and results were extracted in Hyper view and hyper graph. The effect of the air pressure on the servo lever torque is studied and validated with the actual test results. There is good correlation observed on the analysis results with actual test results. The methodology further helped on the design phase of the HVAC kinematic design.</div></div>

<div class="htmlview paragraph">An accelerated comparative exhaust system cycling durability test has been developed at the Ford Motor Company Research and Engineering Center Dynamometer facility. This paper is a summary of events leading up to the development of the test, a description of the test procedures and conditions, the equipment, the actual test results and usage of the test.</div> <div class="htmlview paragraph">The initial design of an exhaust manifold for a new four cylinder engine successfully passed a rather long thermal cycling test program on an engine dynamometer, a test traditionally used in design verification. However, vehicle test results proved unacceptable and necessitated an immediate redesign of the exhaust manifold. Time constraints required a rapid comparative test to evaluate this redesign. Simply modifying the test parameters of the existing thermal cycling test procedure proved inadequate. It was necessary to combine periodic physical loading of the outlet system with thermal cycling to produce the desired results.</div> <div class="htmlview paragraph">Time limitations, equipment availability and economic considerations eliminated a “state of the art” approach to this problem. A more practical method was derived. System loading was accomplished by mounting the test engine on soft vehicle engine mounts and allowing the engine to rock during periodic changes in the engine RPM. The test room exhaust orifice plate and flex hosing [approximately 10.4 Kg (23 lb.)] were mounted on the vehicle exhaust manifold header pipe and partially supported by a spring. During engine rock, the weight would load the exhaust manifold header which, in turn, would load the exhaust manifold. The springs were used to prevent undesirable impact loading of the system.</div> <div class="htmlview paragraph">In an effort to evaluate this mechanical loading, a triaxial accelerometer was mounted on the exhaust manifold for comparative purposes. Five different mounting configurations of the engine were tested for severity and the most severe was used on the test cycle (<span class="xref">Appendix A</span>).</div> <div class="htmlview paragraph">The consistent results of the accelerated durability test supports the continued use of mechanical loading and thermal cycling in comparing exhaust system components and revealing system weaknesses and potential failure modes.</div>

<div class="htmlview paragraph">This paper presents a study of fuel performance in spark ignition engines in relation to abnormal combustion phenomena such as surface ignition and rumble. This was accomplished by observation of the distribution of flame arrivals at ion gaps located within the engine cylinders, or peak pressure position, in terms of crank angle degrees.</div> <div class="htmlview paragraph">By this means, the surface ignition behavior and mass burning rates of LIB (leaded isooctane-benzene) and commercial fuel components were studied in multi-cylinder engines at 10:1 and 12:1 C.R. Additional information was obtained in two instrumented CFR engines operated at 10:1 and 6.75:1 C.R.</div> <div class="htmlview paragraph">It is concluded that the abnormally high peak cylinder pressures giving rise to rumble result from cycles in which combustion occurs early. Early combustion was caused by deposit-ignition of the charge but was also strongly affected by mass burning rate of the charge. Differences in mass burning rate between fuels also affected rumble differently for this reason. Furthermore, the mass burning rate for any fuel tested was greatly increased by the presence of combustion chamber deposits or by finely divided leaded deposits aspirated into the engine.</div> <div class="htmlview paragraph">A large part of the rumble intensity difference noted between the 0 and 100 LIB reference fuels (benzene + 3 cc TEL and iso-octane + 3 cc TEL) may be accounted for by the difference in their burning rates (10-14%). Whether or not this will be a factor in rating rumble by audible means depends on where the ignition timing is set. However, even when allowance is made for burning rate, the 0 LIB fuel shows more early ignitions than 100 LIB in the presence of either accumulated or aspirated deposits. It is, therefore, concluded that these fuels differ also in their tendency to be ignited by deposits.</div> <div class="htmlview paragraph">This information suggests that when rating the rumble tendencies of fuels and engines, a distinction should be made between rumble caused by fuel burning rate differences and that caused by deposit ignition tendency.</div> <div class="htmlview paragraph">Phosphorus added to the fuel in sufficient concentration was found to change the nature of the deposits and thus minimize rumble by reducing deposit-ignition. However, it did not prevent rumble due to early combustion caused by an increased burning rate of the charge.</div> <div class="htmlview paragraph">In a 10:1 C.R. multicylinder engine, significant differences in rumble tendency were found between cylinders. These differences resulted apparently from variations in fuel-air ratio and other factors that could influence the deposits formed and the mass burning rate of the fuel charge.</div>

<div class="htmlview paragraph">In-cylinder reactions of several internal combustion engine configurations were investigated using a highspeed four-spectral infrared (IR) digital imaging device. The study was conducted with a greater emphasis on the preflame processes by mutually comparing results from different engine-fuel systems.</div> <div class="htmlview paragraph">The main features of the methods employed in the study include that the present multi-spectral IR imaging system permits us to capture progressively changing radiation emitted by new species produced in-cylinder fuel-air mixtures prior to being consumed by the heat-releasing reaction fronts.</div> <div class="htmlview paragraph">The study of the Diesel or compression-ignition (CI) engine reactions was performed by varying several parameters, e.g. injection pressures, intake air temperature, fuel air ratio, and the start of injection. They were investigated also for the following mixture preparation-ignition methods: (1) direct-injection of Diesel fuel; (2) homogenous charge (fumigation) ignited by pilot injection and (3) homogeneous charge self-ignition.</div> <div class="htmlview paragraph">For the spark-ignition (SI) engine processes, the reactions were investigated using different fuels including gasoline and propane, which were introduced by either the port-fuel-injection unit or carburetor.</div> <div class="htmlview paragraph">The sequential images captured of in-cylinder preflame reactions were compared with those of the subsequent combustion reactions. In particular, they are expected to serve as an overall survey of visualizing the preflame processes in the cylinder.</div>

<div class="htmlview paragraph">Dowty Aerospace was faced with the problems of maintaining high output at low cost. Production schedules did not allow delays in required plating. With the plating shop located remote from the production area, it was apparent some action had to be taken to insure increased workloads could continue to be met within the scheduled timeframe.</div> <div class="htmlview paragraph"><b>DOWTY AEROSPACE IS A WORLD LEADER</b> in aerospace and defense systems engineering. Dowty companies are well known for the manufacturer of landing gears, propellers, engine fuel controls, flying controls, avionics, general hydraulics, seals, electronic controls and communications. In addition to this manufacturing, Dowty offers repair, overhaul, test and support facilities in all these fields. Dowty also provides full support for other manufacturer's equipment. </div> <div class="htmlview paragraph"> <div class="graphic-wrapper"><img class="article-figure figure" src="890931_fig0001.jpg" alt="No Caption Available"/></div> </div> <div class="htmlview paragraph">Dowty Aerospace Corporation, Product Support Division is located in Sterling, Virginia approximately five miles north of Dulles International Airport. This location includes the corporate offices, equipment and product support for repair and overhaul of components of some 40 different aircraft.</div> <div class="htmlview paragraph">The Dowty plating shop was located in leased facilities approximately seven miles from Corporate headquarters. The leased facilities were not conductive to efficient process layout and utilization for plating. All plating tanks sat on the floor resulting in uneven lip height based on depth of tank. The lack of an overhead material handling system created inefficient parts handling requirements and separation of the plating facility from the machining operation increased transportation costs.</div> <div class="htmlview paragraph">While the quality of plating was excellent and careful planning and coordination allowed meeting production schedules, future growth and flexibility could best be met with the plating shop located closer to the machine shop facilities.</div>

<div class="htmlview paragraph">Lubrication of advanced high temperature engines has been one of the greatest obstacles in the development of the Adiabatic engine. Liquid lubricants which gave lubricating properties as well as heat removal function can no longer carry out this duty when piston ring top ring reversal temperatures approach 540°C. Solid lubricants offer some hope. Since solid lubricants cannot perform the heat removal function, its coefficient of friction must be very low, at least <0.10, in order to prevent heat build up and subsequent destruction to the piston rings and cylinder liners. The Hybrid Piston concept developed in the U.S. Army Advanced Tribology program offers some hope, since the top solid lubricant ring slides over the bottom hydrodynamic lubricant film section during each stroke.</div> <div class="htmlview paragraph">This paper presents the progress made with the solid lubricant top ring in the Hybrid Piston. Four materials have shown promise in the laboratory to fullfil its mission. The characteristic pairs are:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">Detonation Gun (D-Gun) sprayed and densified chrome oxide versus densified plasma sprayed chrome oxide.</div> </li> <li class="list-item"> <div class="htmlview paragraph">Densified plasma sprayed chrome oxide versus densified plasma sprayed Tribaloy T-800.</div> </li> <li class="list-item"> <div class="htmlview paragraph">Densified plasma sprayed iron oxide versus densified plasma sprayed Tribaloy T-800.</div> </li> <li class="list-item"> <div class="htmlview paragraph">Densified Slurry iron oxide versus densified hardened M-2 steel.</div> </li> </ul> </div> <div class="htmlview paragraph">Densification or thermal sealing the plasma spray layer, a process developed on the project, improves the coating's tribological properties. These coating materials are awaiting to be tested in the single cylinder engine.</div>

<div class="section abstract"><div class="htmlview paragraph">This paper presents the design, structural analysis, structural test validation and risk assessment done by Cummins to evaluate the structural integrity of Light Duty engine cylinder head for a Medium Wheelbase (MWB) pick-up truck. Initially, Cummins used the 2.5L and 3.0L (4-cylinder) engines that have standard power ratings based on existing requirements, but rising market demands for more power, fuel efficiency, lower cost and weight, and future emission compliance led to customer requirements for 15% uprate for 2.5L and 22% uprate for 3.0L from the same base engine. The increase in power requirement possesses challenges on critical components, especially cylinder heads in terms of thermal and structural limits.</div><div class="htmlview paragraph">Multiple analysis led design iterations were performed using cutting edge CAE software such as Ansys, Dassault Systems fe-safe, and PTC Creo to ensure the structural integrity of the cylinder head under high thermal and mechanical loads, and to keep design margins within acceptable limits. A key feature identified through topology optimization was diagonal ribbing pattern on each cylinder, which is novel, and similar pattern can be applied to both new and existing engine platforms to enhance stiffness without major changes to the water jacket.</div><div class="htmlview paragraph">The Cylinder head was subjected to a long endurance test, which comprises of high thermal and mechanical loads under extreme operating conditions. After running for specified number of hours as per inhouse test requirements, the engine was stopped for magnetic particle inspection for any signs of fatigue failure.</div><div class="htmlview paragraph">No major cracks were observed on the 3.0L Cylinder head combustion face. However, a few cracks were observed on the 2.5L cylinder head combustion face at exhaust & intake bridges. Upon investigation, it was concluded that crack was due to high thermo-mechanical fatigue loads and hence further optimization was carried out on the cylinder head design. Furthermore, cylinder head gasket coolant orifice optimization is done to improve the coolant distribution to each cylinder. Thermal analysis showed a reduction in exhaust & intake bridge temperature within the acceptable limits. This paper captures the detailed design and structural analysis on 3.0L and 2.5 L diesel engine Cylinder head.</div></div>

<div class="htmlview paragraph">The 5-liter V8 ligth-alloy engine presented by Mercedes-Benz in the new 500 SL at the motor show in Geneva in March 1989 is a new development on the basis of the 8-cylinder engines which have proved themselves for many years.</div> <div class="htmlview paragraph">For this engine, Mercedes-Bens have used a 4-valve light-alloy cylinder head designed in accordance with the most up-to-date features; it has two overhead camshafts per cylinder bank with bucket-type tappets and hydraulic valve clearance compensation. For the first time an electronic/hydraulic adjustment of the intake camshafts is used on a 4-cylinder engine.</div> <div class="htmlview paragraph">This provided the basis for outstanding torque and performance characteristics, stable and smooth idle even at low engine speed, and favourable emission values and fuel consumption figures.</div> <div class="htmlview paragraph">Since the engine consists to a large degree of light alloy, and the power output gained is considerable, it has been possible to attain a weight to power ratio of less than 1 kg/kW.</div>

<div class="htmlview paragraph">Since about four to five years car manufacturers are concerned with measurements of particulate matter in the diesel exhaust gas and with possible measures to control and re duce these substances. This paper discusses the technical approaches to the problems of sampling and determination of the diesel particulates on a mass basis.</div> <div class="htmlview paragraph">In detail the paper includes 1) results from experiences with the instrumentation for sampling and weighing particulate matter: manual sampling set-up, automatic sampling apparatus, filter holder., filter material, and microbalance; 2) results of the investigation of the main test parameters: sample flow rate, background particulate level, filter conditioning and efficiency.</div> <div class="htmlview paragraph">Further, a specific area of concern was the uncertainty of the measurements especially the variability and correlation of test results.</div> <div class="htmlview paragraph">The emission testing program, the basis of this study, comprised the determination of the particulate rates from a number of VW and Audi diesel vehicles with a displacement between 1.5 and 2.4 1 including 4-, 5-, and 6-cylinder engines. These measurements were per formed on a chassis dynamometer in accordance with the specifications of three transient driving cycles including that used in emissions certification, sulfate testing, and highway fuel economy.</div>

<div class="htmlview paragraph">THIS paper deals principally with a description of the methods used in, and a discussion of the results of, an investigation of the possible altitude performance with liquid-cooled engines of high output and consequent high ground boost.</div> <div class="htmlview paragraph">As the first step in the investigation of altitude performance the power of the engine cylinder under all possible conditions of manifold pressure, manifold temperature, and exhaust pressure is determined. The single-cylinder laboratory employed can produce any desired exhaust suction; manifold pressures up to 150 in. hg; inlet air temperature up to 400 F; and handle engine speeds up to 5000 rpm.</div> <div class="htmlview paragraph">Maintenance of power at altitude by means of the exhaust-driven turbo compressor, Mr. DuBois believes, affords a most convenient way out for the engine manufacturer; the troubles, if any, are transferred to the builder of the turbo and of the airplane. He considers “worthy of considerable attention” the use of a two-stage supercharger with an auxiliary engine to drive the first stage. He explains that this arrangement is especially applicable to large airplanes.</div> <div class="htmlview paragraph">Other supercharger arrangements discussed are the single - stage geared compressor; two - speed drives; continuously variable drives; two - stage geared superchargers; and modified two-stage installations, such as two-speed both stages, bypassed first stage, and the two-speed first stage.</div> <div class="htmlview paragraph">The two-speed first-stage method of using two stages is the most satisfactory yet considered, Mr. DuBois believes, since three steps of supercharging reduce the amount of throttling required and, therefore, improve the overall efficiency of the system.</div> <div class="htmlview paragraph"> <div class="graphic-wrapper"><img class="article-figure figure" src="410099_fig0002.jpg" alt="No Caption Available"/></div> </div>

<div class="htmlview paragraph">This paper compares and discusses the impact of conventional and improved start strategies on the design of the exhaust aftertreatment system.</div> <div class="htmlview paragraph">It is recognised that hardware measures on the exhaust side will not be sufficient if Volvo's 5 and 6 cylinder engines are to fulfil SULEV emission levels, assuming passive three way systems only. A new start strategy, providing an excessive heat profile combined with low engine out hydrocarbon emissions, was therefore developed. Temperature profiles, raw emissions and mass flow obtained with the Lean Start Calibration will be shown for the 5 and 6 cylinder engines, both naturally aspirated as turbo.</div> <div class="htmlview paragraph">The remaining part of the paper presents a brief history of the exhaust aftertreatment design modifications for Volvo's 5 cylinder N/A engine fulfilling LEV, ULEV I, ULEV II and PZEV emission levels respectively. The impact of the new start strategy on the cold start performance will be shown. The results will demonstrate the potential of an under floor only system for ULEV II emission levels and a close coupled cascade plus under floor system for PZEV emission levels when the new start strategy is applied. The effect of design parameters such as substrate choice, catalyst volume, … as well as the effect of ageing (both temperature and poisoning), on the cold start and the hot phase emissions will be discussed.</div>

<div class="htmlview paragraph">The effects of the swirl level on the fresh air charge distribution is studied by using a multidimensional computer code for a uniflow type two-cycle diesel engine geometry. The flow is assumed to be axisymmetric. The inlet ports are simulated as an annular opening around the liner, and the exhaust valves are simulated as an annular slot in the cylinder head. Calculations are performed from exhaust valve opening to TDC for a large range of inlet port angles (10-30°). Results are presented in terms of velocity vector plots together with swirl velocity, and fresh charge contour plots.</div> <div class="htmlview paragraph">During the valves open period, the calculations indicate the presence of two vortices in the radial-axial flow plane as previously observed by Diwakar. The first one is near the liner wall (named as wall vortex) and the other is near the symmetry axis (named as the backflow vortex). The incoming fresh air tends to flow toward the cylinder head between these two vortices with reverse flows on the liner wall and near the symmetry axis. Increasing the swirl increases the strength and the region covered by the backflow vortex, redirects the upward fresh charge to a larger radius, and restricts the short-circuiting of the fresh air to the exhaust valves. This increases the trapping of fresh charge and the scavenging efficiency.</div> <div class="htmlview paragraph">Calculations from the exhaust valve closing to TDC show that: <ol class="list nostyle"> <li class="list-item"><span class="li-label">1)</span> <div class="htmlview paragraph">The size of the backflow vortex is reduced as the port is closed and diminishes immediately thereafter. The wall vortex is present up to 60° CA BTDC when the squish effects generated by the piston motion becomes dominant.</div></li> <li class="list-item"><span class="li-label">2)</span> <div class="htmlview paragraph">Fresh charge is not completely mixed with the residual gases even at TDC. There is about 11-17% difference in the fresh charge concentrations at the highest and lowest fresh charge locations at TDC. The inlet port angle (engine swirl level) seems to increase the magnitude of this stratification slightly, but more importantly, it changes the location of this charge stratification considerably. At low swirl levels (port angle 10°), the low fresh charge region is located near the mid-radius of the bowl, and the maximum fresh charge is in the clearance volume between the piston and the bowl. At high swirl levels (port angle 30°), the maximum fresh charge is compressed toward the bowl belly, and the low concentration region is both in the clearance volume and on the cylinder head near the axis. At medium swirl levels (port angle 20), the fresh charge covers the midsection of the bowl, while the residual gases are restricted only within the clearance between piston and engine head.</div></li> </ol></div> <div class="htmlview paragraph">For the diesel engine application and to enhance the mixing of the fuel spray with the fresh air, the residual gas-fresh air stratification pattern of the medium swirl case is better than both the high swirl and low swirl cases.</div> <div class="htmlview paragraph">In addition to the wall vortex (generated by flow separation above the port) and the Backflow Vortex (generated by the swirl velocity field), a new vortex pattern named as the Head Vortex is identified. The mechanism for the Head Vortex development is recognized as the stagnation of the fresh air jet on the cylinder wall rather than on the engine head. The presence of the head vortex changes the mixing rate between the residual gases and the fresh air considerably. The development of the concentration profiles to these final shapes is demonstrated. The effects of the engine swirl level on the mixing of the fresh charge with the residual gases are investigated in terms of the mixing rates and the maximum concentration difference within the flow field.</div>

<div class="htmlview paragraph">An experimental program was conducted to evaluate the contribution of fuel sulfur to brake specific particulate emissions. Three diesel engines - typical for medium and heavy duty truck applications - were tested in four transient cycles of various average loading factors. Three experimental fuels were used having the same basic characteristics, but a sulfur content of 0.05%, 0.19%, and 0.29%, respectively.</div> <div class="htmlview paragraph">Analysis of test results concluded that, among the factors investigated, fuel sulfur was the most important factor contributing to brake specific particulate sulfate variation. For an increase of 0.1% in fuel sulfur, brake specific particulates increase by about 0.025 g/bhp-hr, due to addition of soluble sulfates and bound water. Combustion system, engine type, cycle loading, particulate makeup, had only a weak contribution to the brake specific sulfate variation.</div> <div class="htmlview paragraph">Conversion rates of fuel sulfur to sulfates on particulates were in the range of one to three percent. These results were computed from actual test results and were confirmed by regression analysis of the experimental data.</div>