Showing papers in "SAE transactions in 2004"

Abstract: A consortium of CONCAWE, EUCAR and the EU Commission's JRC carried out a Well-to-Wheels analysis of a wide range of\automotive fuels and powertrains. The study gives an assessment of the energy consumption and greenhouse gas emissions for each pathway. It also considers macroeconomic costs and the market potential of alternative fuels.

Abstract: An experimental study has been carried out to provide qualitative and quantitative insight into gas to wall heat transfer in a gasoline fueled Homogeneous Charge Compression Ignition (HCCI) engine. Fast response thermocouples are embedded in the piston top and cylinder head surface to measure instantaneous wall temperature and heat flux. Heat flux measurements obtained at multiple locations show small spatial variations, thus confirming relative uniformity of incylinder conditions in a HCCI engine operating with premixed charge. Consequently, the spatially-averaged heat flux represents well the global heat transfer from the gas to the combustion chamber walls in the premixed HCCI engine, as confirmed through the gross heat release analysis. Heat flux measurements were used for assessing several existing heat transfer correlations. One of the most popular models, the Woschni expression, was shown to be inadequate for the HCCI engine. The problem is traced back to the flame propagation term which is not appropriate for the HCCI combustion. Subsequently, a modified model is proposed which significantly improves the prediction of heat transfer in a gasoline HCCI engine and shows very good agreement over a range of conditions.

Abstract: Toyota Hybrid System (THS), the powertrain that combines a gasoline engine and an electric motor was first introduced in December 1997. It became the first mass-produced hybrid passenger vehicle in the world, gaining a reputation as a highly innovative vehicle, and its cumulative worldwide sales have exceeded 120,000 units. In 2003, THS had a further evolution. The new-generation Toyota Hybrid System (THS II) would be introduced on the new Prius. This report shall explain THS II, which achieved drastic improvements in power performance and fuel economy, while securing the most stringent emission standard Advanced Technology Partial Zero Emission Vehicle (ATPZEV).

Abstract: Methods of producing non-sooting, low flame temperature diesel combustion were investigated in an optically-accessible, quiescent constant-volume combustion vessel under mixing-controlled diesel combustion conditions. Combustion and soot processes of single, isolated fuel jets were studied after auto-ignition and transient premixed combustion and while the injector was fully-open (i.e. during the mixing-controlled phase of heat release for diesel combustion). The investigation showed that small injector tip orifices could be used to produce non-sooting and low flame temperature combustion simultaneously. The use of small orifices was shown to enable non-sooting and low flame temperature combustion in two different ways as summarized below. A more detailed description of the experimental methods and results is provided in Ref. [1-3]. First, using an injector tip with a 50 micron orifice and ambient oxygen concentrations as low as 10% (simulating the use of extensive EGR), a fuel jet was non-sooting at typical diesel ambient temperatures (1000 K). Second, using the same injector tip at a reduced ambient gas temperature (850 K), but with 21% oxygen, it was shown that non-sooting, mixing-controlled combustion occurred at the lift-off length in a fuel-air mixture with a cross-sectional average equivalence ratio of approximately 0.6-suggesting that the quasi-steady combustion was fuel-lean andmore » thereby avoided the formation of a diffusion flame. The adiabatic flame temperature with reduced ambient oxygen concentration or fuel-lean combustion was approximately 2000 K, compared to typical diesel flame temperatures that exceed 2600 K. The 50 micron orifice results above were obtained using a No.2 diesel fuel. However, using an oxygenated fuel (20 wt% oxygen), the investigation showed that the same low temperature combustion, either with reduced ambient oxygen concentration or fuel-lean combustion, was realized with a 100 micron orifice. Although these single, isolated jets do not have jet-jet interactions that would occur in realistic engines, the results are useful for understanding limiting-case behavior of single-jet mixing and combustion during an injection event. The non-sooting and low flame temperature mixing-controlled combustion realized using small orifice tips suggests that the use of small orifices offers the potential for a simultaneous soot and NOx reduction in an engine, much like diesel HCCI combustion. However, further research is needed to determine whether these methods could be successfully implemented in real engines.« less

Abstract: An investigation has been conducted to determine the relative magnitude of the various factors that cause changes in combustion phasing (or required intake temperature) with changes in fueling rate in HCCI engines These factors include: fuel autoignition chemistry and thermodynamic properties (referred to as fuel chemistry), combustion duration, wall temperatures, residuals, and heat/cooling during induction Based on the insight gained from these results, the potential of fuel stratification to control combustion phasing was also investigated The experiments were conducted in a single-cylinder HCCI engine at 1200 rpm using a GDI-type fuel injector Engine operation was altered in a series of steps to suppress each of the factors affecting combustion phasing with changes in fueling rate, leaving only the effect of fuel chemistry This involved the use of two novel techniques: 1) alternate-firing operation to remove changes in wall temperature and residuals; and 2) a method for determining the effective intake temperature to remove the effect of heating/cooling during induction Three fuels were examined Iso-octane was found to have only a small change in autoignition chemistry with fueling rate; gasoline had a change just slightly larger than iso-octane; and PRF80 had a large change, due to its significant cool-flame chemistry Comparison of the data with chemical-kinetic modeling showed that the detailed iso-octane mechanism matches the trends well, but that the detailed PRF mechanism does not The experimental results indicate that engine management becomes more complicated for fuels with cool-flame chemistry For PRF80, combustion phasing changes immediately with changes in fueling, whereas sudden changes in fueling have little effect on the combustion phasing for iso-octane or gasoline However, the results also show that the potential for ignition control by fuel stratification is much larger for PRF80 Stratification significantly and rapidly shifts combustion phasing with PRF80, but not with iso-octane Charge stratification was also found to be effective for improving combustion efficiency at low-load conditions

Abstract: Investigations of Homogeneous Charge Compression Ignition (HCCI) combustion have been actively conducted as a new combustion technology to substantially and simultaneously reduce NOx and soot to comply with the future stringent exhaust emission regulations. In the past, a method of injecting fuel at the initial stage of the compression stroke has been proposed, but it is known that fuel adheres to the cylinder wall, causing a decline in combustion efficiency and oil dilution. The authors have developed Premixed Compression Ignition (PCI) combustion as a technology of solving the above problem as well as simultaneously reducing NOx and soot. In PCI combustion, fuel is injected into a combustion chamber in the vicinity of the top dead center for preventing fuel from adhering to the wall, and pre-mixture, which is formed shortly before ignition, is burnt. By pre-mixing, this combustion reduces the over-rich region of the mixture to reduce soot emissions, and at the same time lowers the combustion temperature by introducing a large amount of EGR to reduce NOx emissions. This paper reports the result of detailed examination of the basic characteristics of PCI combustion using a single-cylinder engine, and that PCI combustion which uses our investigated approaching can achieve substantial and simultaneous reduction of NOx and soot. This paper also studies the possibility of realizing Split-PCI combustion, which uses the two different combustion modes of PCI combustion and diffusion combustion during one cycle, in high-load operation where application of PCI combustion is restricted by diesel knock. As results of this study, this paper reports that it is available to reduce NOx and soot emissions to a large extent by Split-PCI combustion, even in high-load operation.

Abstract: Two methods for mitigating unacceptably high HCCI heat-release rates are investigated and compared in this combined experimental/CFD work. Retarding the combustion phasing by decreasing the intake temperature is found to have good potential for smoothing heat-release rates and reducing engine knock. There are at least three reasons for this: 1) lower combustion temperatures, 2) less pressure rise when the combustion is occurring during the expansion stroke, and 3) the natural thermal stratification increases around TDC. However, overly retarded combustion leads to unstable operation with partial-burn cycles resulting in high IMEPg variations and increased emissions. Enhanced natural thermal stratification by increased heat-transfer rates was explored by lowering the coolant temperature from 100 to 50°C. This strategy substantially decreased the heat-release rates and lowered the knocking intensity under certain conditions. To further exploit the effect, the heat-transfer rates were further enhanced by increasing the in-cylinder air swirl. This led to even longer combustion durations. Unfortunately, the higher heat losses associated with high air swirl decreased the IMEP g . When the fueling rate was increased to compensate, most of the improvements on the heat-release rates were lost. Overall, combustion phasing retard was found to have better potential for smoothing heat-release rates than enhancing the thermal stratification by the means considered in this work. However, operation with highly retarded combustion requires precise control of the ignition timing. Furthermore, it is found that the acceptable intake temperature range narrows rapidly with increasing equivalence ratio. Above a certain fueling rate a steady state operating point cannot be established by setting the intake temperature to a fixed value. This problem is caused by wall heating and the coupling between wall temperature and combustion phasing.

Abstract: In Europe, over recent years, there has been a marked shift in the regulatory approach to ensuring system safety. Whereas compliance with prescriptive safety codes and standards was previously the norm, the responsibility has now shifted back onto the developers and operators to construct and present well reasoned arguments that their systems achieve acceptable levels of safety. These arguments (together with supporting evidence) are typically referred to as a safety case. This paper describes the role and purpose of a safety case (as defined by current safety and regulatory standards). Safety arguments within safety cases are often poorly communicated. This paper presents a technique called GSN (Goal Structuring Notation) that is increasingly being used in safety-critical industries to improve the structure, rigor, and clarity of safety arguments. Based upon the GSN approach, the paper also describes how an evolutionary and systematic approach to safety case construction, in step with system development, can be facilitated.

Abstract: Combustion phasing is one important issue that must be addressed for HCCI operation. The intake temperature can be adjusted to achieve ignition at the desired crank angle. However, heat-transfer during induction will make the effective intake temperature different from the temperature measured in the runner. Also, depending on the engine speed and port configuration, dynamic flow effects cause various degrees of charge heating. Additionally, residuals from the previous cycle can have significant influence on the charge temperature at the beginning of the compression stroke. Finally, direct injection of fuel will influence the charge temperature since heat is needed for vaporization. This study investigates these effects in a systematic manner with a combination of experiment and cycle simulation using WAVE from Ricardo. The results show that the amount of charge heating/cooling that occurs due to heat-transfer during the induction period can be computed from changes in the volumetric efficiency. The amount of charge cooling associated with vaporization of directly injected fuel changes with injection timing and can be related to the volumetric efficiency. A simple procedure for estimating the charge mixture temperature at the end of the intake stroke is presented. Several examples are given where this procedure can be used beneficially to explain experimental observations for fired HCCI operation where the charge temperature at the end of the intake stroke was related to the combustion phasing. Iso-octane was used as a gasoline surrogate since it facilitates comparison with chemical-kinetics models, in this case the detailed iso-octane mechanism from LLNL. Although this procedure is developed for HCCI operation, it can be applied to other types of engines as well. For example, the changes to the charge temperature that occur during the induction process are important for both tH'e occurrence of knock in Sl engines and NO x formation in Diesel engines.

Abstract: The laminar burning velocities of 45 hydrocarbons have been investigated in a constant volume combustion vessel at elevated temperature and pressure. The mixtures are ignited in the center of a spherical vessel at an initial temperature of 450 K and pressure of 304 kPa. Data have been acquired over the stoichiometry range of 0.55 ≤ φ ≤ 1.4. The burning velocity is determined from a thermodynamic analysis of the pressure vs. time data. The results for alkanes and alkenes are consistent with trends previously identified in the literature, i.e., alkenes are faster than the corresponding alkane with the same carbon connectivity. For both alkanes and alkenes, branching lowers the burning velocity. In addition, terminal alkenes and alkynes are found to be slightly faster than internal alkenes and alkynes. The present study includes broader coverage of aromatics than previous literature reports. The burning velocities for aromatics show a strong dependence on the type and site of alkyl substitution; methyl substitution lowers the burning velocity more than substitution with larger alkyl groups. For multiple methyl group substitution, meta substitution lowers the burning velocity more than ortho/para. The physical and chemical kinetic bases for the variation of burning velocity with molecular structure are discussed with the aid of elemental flux analyses of simulations using detailed chemical kinetic mechanisms. A consistent trend is identified in which "fast" burning fuels have a higher flux into decomposition pathways that yield H atoms and C2 fragments, while "slow" fuels have a higher flux into pathways that form CH3 radicals. The data and analysis presented in this paper provide a comprehensive, fundamental basis for relating fuel structure effects to combustion efficiency and emissions.

Abstract: Reducing engine swept volume (so-called 'downsizing') offers the potential to meet future tighter CAFE standards and reduced CO 2 vehicle emissions in Europe. In downsizing the gasoline engine, a key challenge is controlling octane requirement without sacrificing fuel economy. The authors have investigated five alternative approaches on a turbocharged Dl gasoline engine: ○ Conventional stoichiometric operation, with reduced compression ratio (CR) ○ Lean Boost Dl (LBDI) with lean operation at full-load to control octane requirement while maintaining a high CR ○ EGR Boost with cooled EGR dilution rather than excess air to control octane requirement ○ Miller cycle concept, where valve-timing strategies are employed to reduce the effective compression ratio at high load ○ Dual injection strategies to control octane requirement Each approach has been investigated using engine performance and vehicle simulation codes. Experimental investigations have been carried out using a 1.125L 13 multi-cylinder engine. The most promising concept, LBDI, has been further developed using the multi-cylinder engine installed in a Ford Focus C-class vehicle.

Abstract: 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. Advanced turbocharging technology for gasoline engines is discussed including cold start emissions (catalyst light-off), high temperature materials, variable geometry mechanisms and electrically assisted turbocharging. It is shown that these technologies combined with an appropriate control logic can yield great benefits in driveability while at the same time giving all the fuel economy, weight and packaging benefits of engine downsizing.

Abstract: A method to curtail emissions of smoke and other pollutants from diesel engines is to enhance the oxygen supply to their combustion chamber. This can be accomplished by enriching either the intake air stream or the fuel stream with oxygen. Experimental studies concerning the oxygen-enrichment of intake air, have revealed large decrease of ignition delay, drastic decrease of soot emissions as well as reduction of CO and HC emissions while, brake specific fuel consumption (BSFC) remained unaffected and increasing of power output is feasible. However, this technique was accompanied by considerable increase of NO x emissions. Experimental and theoretical studies with oxygenated fuels have demonstrated large decrease of soot emissions, which correlated well with the fuel oxygen content. Reduction of CO and HC emissions with oxygenated fuels was also obtained. However, penalties in both BSFC and NO x emissions have been observed with oxygenation of diesel fuels. In both cases one has to weigh the tradeoffs in fuel economy, in power output and in the emissions of various pollutants. Moreover, fuel cost, availability and supply infrastructure, as well as equipment and operational costs, are among concerns that apply to these techniques. This manuscript presents a comparative evaluation of the two techniques regarding engine performance characteristics, environmental repercussions and economy of operation. The primary objective is to contrast the benefits and the drawbacks of the two techniques in view of economic, operational and environmental parameters. Results have shown that the overall economy of operation of the two techniques may be comparable, if the price of oxygenated fuel blends is similar to that of diesel fuel. Their impact on pollutant emissions may also be comparable, if the oxygen enrichment of either technique is limited to a low level (<23% by mass in the cylinder mixture). However, there are possibilities of increasing the power density of engines with oxygen enrichment of the intake air.

Abstract: One of the major problems in the CFD simulation of Diesel sprays is the incomplete and inadequate specification of initial conditions for the spray droplets. This is mainly a consequence of lack of understanding of the atomization process, which has inhibited the development of sufficiently general and accurate models for use in engine combustion simulations. In this paper a novel CFD approach, combining multiphase volume-of-fluid (VOF) and large eddy simulation (LES) methodologies, is used to perform quasi-direct transient fully three dimensional calculations of the atomization of a high-pressure diesel jet, providing detailed information on the processes and structures in the near nozzle region. The methodology allows separate examination of diverse influences on the breakup process and is expected in due course to provide a detailed picture of the mechanisms that govern the spray formation. It will therefore be a powerful tool for assisting in the development of accurate atomization models for practical applications. Our investigations so far have focused on the performance and initial validation of the methodology, in the absence of cavitation.

Abstract: ABCTRACT The reduction of particulate emissions limits requires new tools for the tuning of engines and exhaust aftertreatment systems. Time-resolved monitoring of low soot emissions is a key feature for such developments. The paper describes an improved photoacoustic soot sensor, and presents its applications for the characterization of transient exhaust soot emissions before and after Diesel emission after-treatment systems. The detection limit of the unit is around 5 μg/m 3 soot, which is two orders of magnitude better than conventional time-resolved transmission measurement. Additionally, a wide dynamic range of four orders of magnitude can be achieved without range switching. The photoacoustic signal is proportional to the soot mass, no significant cross-sensitivities to gaseous absorbers were detected.

Abstract: The authors would like to appreciate the support by the national research laboratory scheme, Korea and in part by the Brain Korea 21 Project.

Abstract: Predictive Cruise Control (PCC) is a system that enhances and works in combination with the existing Conventional Cruise Control. Based on elevation information captured in a 3D map and a predictive algorithm, PCC allows the vehicle speed to vary around the cruise control set speed within a defined speed band in an effort to reduce fuel consumption. As fuel consumption is a major portion of a truck's life cycle costs (LCC) and cruise control is used extensively in the United States and Canada, PCC can significantly reduce the truck's LCC.

Abstract: A single cylinder CFR research engine has been run in HCCI combustion mode at the rich and the lean limits of the homogeneous charge operating range. To achieve a variation of the degree of charge stratification, two GDI injectors were installed: one was used for generating a homogeneous mixture in the intake system, and the other was mounted directly into the side of the combustion chamber. At the lean limit of the operating range, stratification showed a tremendous improvement in IMEP and emissions. At the rich limit, however, the stratification was limited by the high-pressure rise rate and high CO and NOx emissions. In this experiment the location of the Dl injector was in such a position that the operating range that could be investigated was limited due to liquid fuel impingement onto the piston and liner.

Abstract: Experiments were performed to identify the knock trends of lean hydrocarbon-air mixtures, and such mixtures enhanced with hydrogen (H 2 ) and carbon monoxide (CO). These enhanced mixtures simulated 15% and 30% of the engine's gasoline being reformed in a plasmatron fuel reformer [1]. Knock trends were determined by measuring the octane number (ON) of the primary reference fuel (mixture of isooctane and n-heptane) supplied to the engine that just produced audible knock. Experimental results show that leaner operation does not decrease the knock tendency of an engine under conditions where a fixed output torque is maintained; rather it slightly increases the octane requirement. The knock tendency does decrease with lean operation when the intake pressure is held constant, but engine torque is then reduced. When H 2 and CO are added to the mixture, the knock susceptibility is reduced, as illustrated by a decrease in the measured octane number of the primary reference fuel resulting in knock. Experiments conducted with the addition of H 2 and CO separately show similar trends, but to a lesser degree; therefore, both H 2 and CO act as octane enhancers when added to a hydrocarbon-air mixture. The extent to which H 2 and CO improve the knock resistance of a mixture can be estimated by finding the bond-weighted octane numbers for these non-traditional blends of fuels. To understand these results better, a reduced chemical kinetic model was also used to predict autoignition of the end-gas for various conditions and fuel-air mixtures. Predicted model trends of knock onset of primary reference fuels agree with experimental observations. A comprehensive isooctane chemistry mechanism was used to demonstrate that H 2 and CO are effective in lengthening the ignition delay, thereby reducing knock tendency.

Abstract: In the HCCI Engine, inhomogeneity in fuel distribution and temperature in the pre-mixture exists microscopically, and has the possibility of affecting the ignition and combustion process. In this study, the effect of charge inhomogeneity in fuel distribution on the HCCI combustion process was investigated. Two-dimensional images of the chemiluminescence were captured by using a framing camera with an optically accessible engine in order to understand the spatial distribution of the combustion. DME was used as a test fuel. By changing a device for mixing air and fuel in the intake manifold, inhomogeneity in fuel distribution in the pre-mixture was varied. The result shows that luminescence is observed in a very short time in a large part of the combustion chamber under the homogeneous condition, while luminescence appears locally with considerable time differences under the inhomogeneous condition. It is also shown that the local luminescence durations are almost the same in both conditions.

Abstract: Experiments were conducted with a commercially available six-cylinder, 4-valves per cylinder, turbocharged, direct injection (Dl) diesel engine. The engine was operated with low sulfur diesel fuel, ultra low sulfur diesel fuel and two other blends, low sulfur diesel fuel with 20 wt.% biodiesel and ultra low sulfur diesel fuel with 20 wt.% biodiesel, to investigate the effect of the base fuels and their blends on combustion and emissions. Combustion analysis, particulate matter emissions and exhaust gas composition (CO, NO x and total hydrocarbons) were determined at eight steady-state operating conditions according to the AVL 8-Mode test protocol. Combustion analysis showed at high load conditions a retarded start of injection, an earlier start of combustion and a lower premixed burn peak with ultra low sulfur diesel fuel. Mode averaged NO x emissions decreased with ultra low sulfur diesel fuel and biodiesel blends compared to low sulfur diesel fuel. A 20% PM reduction was observed with ultra low sulfur (15 PPM) diesel fuel compared to low sulfur (325 PPM) diesel fuel.

Abstract: It is generally accepted that exhaust NO x emissions of diesel engines increase with the degree of premixed burning. Although several mechanisms proposed in the literature are likely responsible for some aspects of the correlation, taken together, they cannot explain all observations of this correlation. In this study, thermodynamic analyses and optical/imaging diagnostics were employed in an optically-accessible, heavy-duty Dl diesel engine to examine the in-cylinder mechanisms by which fuel/air premixing affects engine-out NO x emissions. Exhaust NO and NO x emissions were measured and correlated with observations of soot luminosity and jet penetration as the intake-temperature and injection timing were varied The engine was operated at low-load conditions, for which the premixed burn was a significant fraction of the total heat released. As injection timing was retarded to the misfire limit, dramatic reductions in soot luminosity accompanied increased exhaust NO x emissions, even as the calculated adiabatic flame temperatures decreased. Since thermal NO formation increases with temperature, the reduction of the cooling effect of soot radiative heat transfer may increase the actual flame temperature, and thus NO formation, as the jets become less sooty. Compression heating of the reactant mixture by the large pressure rise during premixed combustion was found to be insufficient to explain exhaust NO x trends. Compression of post-flame burned-gases, however, could be responsible for some aspects of the correlation. Though the products of the premixed burn are normally too rich to form significant thermal NO, under very long ignition-delay conditions, portions of the mixture at ignition may be lean enough for significant thermal NO formation.

Abstract: A series of calibration methodologies have been developed to aid the powertrain engineer in meeting calibration targets throughout the engine development process, i.e. from early engine mapping through to final OBD calibration and vehicle sign off. This paper will present practical examples of the methodologies developed for the base engine mapping phase. The advantages of using design of experiments and advanced statistical modelling to develop empirical models are shown. The models are used to populate the powertrain control module calibration tables as well as for predictive emissions optimisation. The major benefit of the calibration methodologies utilising the model based approach is the ability to evaluate the drive/emissions compromise with no additional testing.

Abstract: This paper presents an overview of the results on heavy duty engines collected in the “PARTICULATES” project, which aimed at the characterization of exhaust particle emissions from road vehicles. The same exhaust gas sampling and measurement system as employed for the measurements on light duty vehicles [1] was used. Measurements were made in three labs to evaluate a wide range of particulate properties with a range of heavy duty engines and fuels. The measured properties included particle number, with focus separately on nucleation mode and solid particles, particle active surface and total mass. The sample consisted of 10 engines, ranging from Euro-I to prototype Euro-V technologies. The same core diesel fuels were used as in the light duty programme, mainly differentiated with respect to their sulphur content . Additional fuels were tested by some partners to extend the knowledge base. Engine tests were mainly conducted over the standard European regulatory cycles (ESC and ETC), although additional steady state conditions, including some offcycle points, were also assessed. All data (both real time and integrated) were collected in a common data base and centrally analyzed, using common formats and methodologies in order to eliminate inconsistencies and optimize comparability. As for light duty vehicles, the results show that particulate emissions from heavy duty engines are markedly reduced by advanced technologies, most notably by the combination of particulate traps and sulphur-free fuels. However, particulate emissions patterns are also shown to be influenced by operating conditions; in particular fuel sulphur effects are most obvious under high temperature operation. The study provides evidence that particulate number measurement offers the potential for greater sensitivity in evaluating particulate emissions. It demonstrates that the “PARTICULATES” dedicated sampling procedure is capable of delivering repeatable results even in the case of the unstable nucleation mode, also for heavy duty engines. The data provide a first step towards emission factors based on particle size and number for heavy duty engines. However it should not be forgotten that nucleation mode particles are highly dependent on sampling conditions. Further research continues to be needed on the health relevance of measurements of “nucleation” mode particles, their chemical composition and their fate in the atmosphere.

Abstract: Schemes to extend the operational region of gasoline compression ignition were explored using single (optial) and 4-cylinder 4-stroke engines equipped with an electromagnetic valve train. This report focuses mainly on the use of direct fuel injection devices (multi-hole and pintle types),exhaust gas recirculation (EGR) through valve timing, and their effects on the compression ignition operating ranges, and emissions. Also considered is charge boost HCCI using a mechanical supercharger. The results indicated that use of either direct fuel injection or charge boost increased (relative to homogeneous charge operation using port injection) the upper load range from an IMEP peak of about 400 kPa to 650 kPa, but the use of direct fuel injection deteriorated both the co-variation in IMEP (up to about 6%) and the NO x emission levels (up to about 8 g/kWh). In contrast, charge boost retained the very low NOx emission levels of port injection HCCI. At the lower load range, a small amount of fuel injection during negative valve overlap expanded the operational range at the lower load range. It is presumed that the EGR with negative valve overlap has a similar effect as injection during negative overlap namely the oxidation of residual unburned hydrocarbons from the prior cycle during this period. This facilitates compression ignition.

Abstract: This paper proposes an advanced control strategy to improve vehicle handling and directional stability by integrating either Active Front Steering (AFS) or Active Rear Steering (ARS) with Variable Torque Distribution (VTD) control. Both AFS and ARS serve as the steerability controller and are designed to achieve the improved yaw rate tracking in low to mid-range lateral acceleration using Sliding Mode Control (SMC); while VTD is used as the stability controller and employs differential driving torque between left and right wheels on the same axle to produce a relatively large stabilizing yaw moment when the vehicle states (sideslip angle and its angular velocity) exceed the reference stable region defined in the phase plane. Based on these stand-alone subsystems, an integrated control scheme which coordinates the control actions of both AFS/ARS and VTD is proposed. The functional difference between AFS and ARS when integrated with VTD is explained physically. The effect of the integrated control system on the vehicle handling characteristics and directional stability is studied through an open loop computer simulation of an eight degrees of freedom nonlinear vehicle model. Simulation results confirm the effectiveness of the proposed control system and the overall improvements in vehicle handling and directional stability.

Abstract: Calibration of engine management systems requires considerable engineering resources during the development of modern engines. Traditional calibration methods use a combination of engine dynamometer and vehicle testing, but pressure to reduce powertrain development cost and time is driving development of more advanced calibration techniques. In addition, future engines will feature new technology, such as variable valve actuation, that is necessary to improve fuel economy, performance, and emissions. This introduces a greater level of system complexity and greatly increases test requirements to achieve successful calibrations. To address these problems, new simulation tools and procedures have been developed within Delphi to rapidly generate optimized calibration maps. The objective of the work is to reduce calibration effort while fully realizing the potential benefit from advanced engine technology. The procedure utilizes GT Power engine simulation software and engine models validated through limited dynamometer testing. A front end to GT Power was written to automatically call GT Power executables and produce the calibration dataset. Several methods were used to accelerate the simulation process. Calibrations are optimized using an additional software tool that includes a weighted-optimization scheme. User-defined constraints may be applied during optimization for cam phaser position, combustion dilute limits, exhaust temperature or any other variable defined in the engine model. The overall procedure includes vehicle simulation using ADVISOR to estimate fuel economy and emissions for the drive cycle.

Abstract: On the basis of the molecular thermodynamics for fluids, the thermodynamic properties of DME are developed for pressure p < 500 bar and temperature T ≤ 200 °C, which covers pressures and temperatures that a DME fuel system for the Cl-engine application would experience. The properties cover subcooled, two-phase, and superheated/supercritical regions, including p-v-T properties, enthalpy, entropy, latent heat, heat capacity, speed of sound in vapor, liquid and two-phase mixtures, bulk modulus, and surface tension. A volume-cubic equation of state for DME also is developed, which allows calculating the DME density at any given pressure and temperature analytically. All the properties are given in equations as well as in charts. For convenience in two-phase-flow applications, e.g., design of the fuel tank and cavitation analysis, the saturated properties are also given in tables, listed in both pressure and temperature up to the critical point. Because they are derived on the basis of the general thermodynamic theories, these properties have a reasonable accuracy; thus, they can be used as reliable estimations when the experimental data are unavailable. For the two-phase regions, the calculated properties are compared with available experimental data reported in the literature and excellent agreements are observed. Comparisons between diesel fuel and DME are conducted on the properties affecting the engine fuel management. Thermochemical properties for the DME-air mixture and characteristics of the exhaust from DME combustion are also analyzed. Finally, to facilitate the DME fuel system design and modeling, the transport properties from the authors' previous work, such as viscosity, thermal conductivity and Prandtl number for liquid DME, are included in the paper, making this paper a rich source for DME properties.

Abstract: The 2007 emission standards for both light-duty and heavy-duty diesel vehicles remain a challenge. A level of about 90% NOx conversion is required to meet the standards. Technologies that have the most potential to achieve very high NOx conversion at low temperatures of diesel exhaust are lean NOx traps (LNTs) and Selective Catalytic Reduction (SCR) of NOx using aqueous urea, typically known as Urea SCR. The LNT has the advantage of requiring no new infrastructure, and does not pose any new customer compliance issues. However, Urea SCR has high and durable NOx conversion in a wider temperature window, a lower equivalent fuel penalty, and lower system cost. On a technical basis, Urea SCR has the best chance of meeting the 2007 NOx targets. This paper reviews the results of some demonstration programs for both light-and heavy-duty applications.

Abstract: Natural gas has a high auto-ignition temperature, requiring high compression ratios and/or intake charge heating to achieve HCCI (homogeneous charge compression ignition) engine operation. Previous work by the authors has shown that hydrogen addition improves combustion stability in various difficult combustion conditions. It is shown here that hydrogen, together with residual gas trapping, helps also in lowering the intake temperature required for HCCI. It has been argued in literature that the addition of hydrogen advances the start of combustion in the cylinder. This would translate into the lowering of the minimum intake temperature required for auto-ignition to occur during the compression stroke. The experimental results of this work show that, with hydrogen replacing part of the fuel, a decrease in intake air temperature requirement is observed for a range of engine loads, with larger reductions in temperature noted at lower loads. It is also shown that the low NOx emissions and high rates of heat release, typical for HCCI, are retained with hydrogen-assisted operation, especially at low engine loads. A practical possibility of producing the necessary hydrogen in a fuel reformer fitted in the exhaust gas recirculation system is illustrated for one engine condition.