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When increasing EGR from low levels to a level that corresponds to low temperature combustion, soot emissions initially increase due to lower soot oxidation before decreasing to almost zero due to very low soot formation. At the EGR level where soot emissions start to increase, the NOx emissions are low, but not sufficiently low to comply with future emission standards and at the EGR level where low temperature combustion occurs CO and HC emissions are too high. The purpose of this study was to investigate the possibilities for shifting the so-called soot bump (where soot levels are increased) to higher EGR levels, or to reduce the magnitude of the soot bump using very high injection pressures (up to 240 MPa) while reducing the NOx emissions using EGR. The possibility of reducing the CO and HC emissions at high EGR levels due to the increased mixing caused by higher injection pressure was also investigated and the flame was visualized using an endoscope at chosen EGR values.

Studies have shown that premixed combustion concepts such as PCCI and RCCI can achieve high efficiencies while maintaining low NOx and soot emissions. The RCCI (Reactivity Controlled Compression Ignition) concept use blending port-injected high-octane fuel with early direct injected high-cetane fuel to control auto-ignition. This paper describes studies on RCCI combustion using CNG and diesel as the high-octane and high-cetane fuels, respectively. The test was conducted on a heavy-duty single cylinder engine. The influence of injection timing and duration of the diesel injections was examined at 9 bar BMEP and1200 rpm. In addition, experiments were conducted using two different compression ratios, (14 and 17) with different loads and engine speeds. Results show both low NOx and almost zero soot emissions can be achieved but at the expense of increasing of unburned hydrocarbon emissions which could potentially be removed by catalytic after-treatment.

Gasoline and gasoline-ethanol sprays from an outward-opening piezo-injector were studied in a constant volume/pressure chamber using high-speed imaging and phase doppler anemometry (PDA) under stratified cold start conditions corresponding to a vehicle ambient temperature of 243 K (−30°C/−22°F); in-cylinder air pressure of 5 bar, air temperature of 350 K (−30°C/−22°F) and fuel temperature of 243 K. The effects of varying in-cylinder pressure and temperature, fuel injection pressure and fuel temperature on the formation of gasoline, E75 and pure ethanol sprays were investigated. The results indicate that fuel composition affects spray behaviour, but less than expected. Furthermore, varying the temperature of the fuel or the air surrounding the spray also had minor effects. As expected, the fuel injection pressure was found to have the strongest influence on spray formation under stratified conditions.

Future pressures to reduce the fuel consumption of passenger cars may require the exploitation of alternative combustion strategies for gasoline engines to replace, or use in combination with the conventional stoichiometric spark ignition (SSI) strategy. Possible options include homogeneous lean charge spark ignition (HLCSI), stratified charge spark ignition (SCSI) and homogeneous charge compression ignition (HCCI), all of which are intended to reduce pumping and thermal losses. In the work presented here four different combustion strategies were evaluated using the same engine: SSI, HLCSI, SCSI and HCCI. HLCSI was achieved by early injection and operating the engine lean, close to its stability limits. SCSI was achieved using the spray-guided technique with a centrally placed multi-hole injector and spark-plug. HCCI was achieved using a negative valve overlap to trap hot residuals and thus generate auto-ignition temperatures at the end of the compression stroke.

During 1991 Volvo Car Corporation has introduced the new Volvo 850 GLT model featuring front wheel drive with transverse installation of the engine and gearbox. The powertrain; consists of a new in-line five-cylinder engine in combination with a four speed electronically controlled automatic gearbox or a five speed manual gearbox. The engine features DOHC 20 valves, V-VIS (Volvo Variable Induction System), well tuned exhaust system and microprocessor controlled engine management systems. The engine was designed and developed as a new member of Volvo's modular engine family. The first member was the in-line six-cylinder engine B6304F [1] introduced in 1990. The modular engines have a large number of identical components and the major components are machined in common transfer lines which makes the manufacturing process highly rational and cost-effective.

In order to investigate the effects of split injection on emission formation and engine performance, experiments were carried out using a heavy duty single cylinder diesel engine. Split injections with varied dwell time and start of injection were investigated and compared with single injection cases. In order to isolate the effect of the selected parameters, other variables were kept constant. In this investigation no EGR was used. The engine was equipped with a common rail injection system with a piezo-electric injector. To interpret the observed phenomena, engine CFD simulations using the KIVA-3V code were also made. The results show that reductions in NOx emissions and brake specific fuel consumption were achieved for short dwell times whereas they both were increased when the dwell time was prolonged. No EGR was used so the soot levels were already very low in the cases of single injections.

Eight different cylinder pressure trace based knock detection methods are compared using two reference cycles of different time-frequency content, reflecting single blast and developing blast, and a test population of 300 knocking cycles. It is shown that the choice of the pass window used for the pressure data has no significant effect on the results of the different methods, except for the KI20. In contrast to other authors, no sudden step in the knock characteristics is expected; first, because the data investigated contain only knocking cycles, and second, because a smooth transition between normal combustion and knock is expected, according to recent knock theory. It is not only the correlation coefficient, but also the Kendall coefficient of concordance, that is used to investigate the differences between the knock classification methods.

Combustion characteristics of dimethyl ether, DME, have been investigated experimentally, in a heavy duty single cylinder engine equipped with an adapted common rail fuel injection system, and the effects of varying injection timing, rail pressure and exhaust gas recirculation on the combustion and emission parameters. The results show that DME combustion does not produce soot and with the use of exhaust gas recirculation NOX emissions can also be reduced to very low levels. However, high injection pressure and/or a DME adopted combustion system is required to improve the mixing process and thus reduce the combustion duration and carbon monoxide emissions.

Cycle-resolved end-gas temperatures were measured using dual-broadband rotational CARS in a single-cylinder spark-ignition engine. Simultaneous cylinder pressure measurements were used as an indicator for knock and as input data to numerical calculations. The chemical processes in the end-gas have been analysed with a detailed kinetic mechanism for mixtures of iso-octane and n-heptane at different Research Octane Numbers (RON'S). The end-gas is modelled as a homogeneous reactor that is compressed or expanded by the piston movement and the flame propagation in the cylinder. The calculated temperatures are in agreement with the temperatures evaluated from CARS measurements. It is found that calculations with different RON'S of the fuel lead to different levels of radical concentrations in the end-gas. The apperance of the first stage of the autoignition process is marginally influenced by the RON, while the ignition delay of the second stage is increased with increasing RON.

Experiments were performed using a Light-Duty, single-cylinder, research engine in which the emissions, fuel consumption and combustion characteristics of two Fischer-Tropsch (F-T) Diesel fuels derived from natural gas and two conventional Diesel fuels (Swedish low sulfur Diesel and European EN 590 Diesel) were compared. Due to their low aromatic contents combustion with the F-T Diesel fuels resulted in lower soot emissions than combustion with the conventional Diesel fuels. The hydrocarbon emissions were also significantly lower with F-T fuel combustion. Moreover the F-T fuels tended to yield lower CO emissions than the conventional Diesel fuels. The low emissions from the F-T Diesel fuels, and the potential for producing such fuels from biomass, are powerful reason for future interest and research in this field.

This work evaluates the effect of charge stratification on combustion phasing, rate of heat release and emissions for HCCI combustion. Engine experiments in both optical and traditional single cylinder engines were carried out with PRF50 as fuel. The amount of stratification as well as injection timing of the stratified charge was varied. It was found that a stratified charge can influence combustion phasing, increasing the stratification amount or late injection timing of the stratified charge leads to an advanced CA50 timing. The NOx emissions follows the CA50 advancement, advanced CA50 timing leads to higher NOx emissions. Correlation between CA50 can also be seen for HC and CO emissions when the injection timing was varied, late injection and thereby advanced CA50 timing leads to both lower HC and CO emissions.

When increasing EGR from low levels to levels corresponding to low temperature combustion, soot emissions first start to increase (due to reductions in soot oxidation), before decreasing to almost zero (due to very low rates of soot formation). At the EGR level where soot emissions start to increase, the NOx emissions are still low, but not low enough to comply with future emission standards. The purpose of this study was therefore to investigate the possibilities for moving the so-called “soot bump” (increase in soot) to higher EGR levels or reducing the magnitude of the soot bump. This involved an experimental investigation of parameters affecting the combustion and thus the engine-out emissions. The parameters investigated were: charge air pressure, injection pressure, EGR temperature and post injection (with different dwell times) for a wide range of EGR rates.

The effect of ammoniac deoxidizing agent (Urea) on the reduction of NOx produced in the Diesel engine was investigated numerically. Urea desolved in water was directly injected into the engine cylinder during the expansion stroke. The NOx deoxidizing process was described using a simplified chemical kinetic model coupled with the comprehensive kinetics of Diesel oil surrogate combustion. If the technology of DWI (Direct Water Injection) with the later injection timing is supposed to be used, the deoxidizing reactants could be delivered in a controlled amount directly into the flame plume zones, where NOx are forming. Numerical simulations for the Isotta Fraschini DI Diesel engine are carried out using the KIVA-3V code, modified to account for the “co-fuel” injection and reaction with combustion products. The results showed that the amount of NOx could be substantially reduced up to 80% with the injection timing and the fraction of Urea in the solution optimized.

The emissions from a direct injection diesel engine measured according to the ECE R49 13-mode cycle and as a function of exhaust gas recirculation are compared for diesel fuel without water addition, and for water-in-diesel as emulsion and microemulsion. The effect of water addition on the soot emissions was remarkably strong for both the emulsion and microemulsion fuels. The average weighted soot emission values for the 13-mode cycle were 0.0024 and 0.0023 g/kWh for the two most interesting emulsion and microemulsion fuels tested, respectively; 5-fold lower than the US 2007 emission limit.

The spray formation and consequent atomization of an outward opening piezo-electric gasoline DI injector have been experimentally investigated in a constant pressure spray chamber. The sizes and velocities of the droplets and the resulting spray shape were evaluated, under different boundary conditions, using Planar Mie scattering and Planar Laser-induced Fluorescence (PLIF) in combination with Phase Doppler Anemometry (PDA) analyses and high-speed video photography. The use of piezo-electric actuation for gasoline DI injectors provides an additional means to control the atomization and spray shape that is not available with solenoid-driven injectors such as swirling and multi-hole type injectors. For instance, with piezo injectors up to four injections per cycle are possible, and the fuel flow rate can be controlled by adjusting needle lift. The captured high-speed video images show that a hollow-cone spray forms as the fuel exits the outward-opening nozzle.

In order to meet future emissions legislation for Diesel engines and reduce their CO2 emissions it is necessary to improve diesel combustion by reducing the emissions it generates, while maintaining high efficiency and low fuel consumption. Advanced injection strategies offer possible ways to improve the trade-offs between NOx, PM and fuel consumption. In particular, use of high EGR levels (⥸ 40%) together with multiple injection strategies provides possibilities to reduce both engine-out NOx and soot emissions. Comparisons of optical engine measurements with CFD simulations enable detailed analysis of such combustion concepts. Thus, CFD simulations are important aids to understanding combustion phenomena, but the models used need to be able to model cases with advanced injection strategies.

Optical studies of combusting diesel sprays were done on three different alternative liquid fuels and compared to Swedish environmental class 1 diesel fuel (MK1). The alternative fuels were Rapeseed Oil Methyl Ester (RME), Palm Oil Methyl Ester (PME) and Fischer-Tropsch (FT) fuel. The studies were carried out in the Chalmers High Pressure High Temperature spray rig under conditions similar to those prevailing in a direct-injected diesel engine prior to injection. High speed shadowgraphs were acquired to measure the penetration of the continuous liquid phase, droplets and ligaments, and vapor penetration. Flame temperatures and relative soot concentrations were measured by emission based, line-of-sight, optical methods. A comparison between previous engine tests and spray rig experiments was conducted in order to provide a deeper explanation of the combustion phenomena in the engine tests.

In the study reported here the combustion and emission characteristics of a heavy duty six-cylinder diesel engine fuelled with dimethyl ether (DME) of chemical grade and DME with small and varying amounts of methanol and/or water were experimentally investigated. In addition, the size distribution of emitted particles and selected unregulated emissions were sampled. Methanol and water additions had a very limited effect on emissions, but affected the combustion processes in a way that accentuated the premixed combustion and thus caused more energy to be released early in the cycle. At high load, however, the effect was reversed, due to the lack of distinct premixed combustion. The results confirm that DME combustion does not generate any accumulation mode particles. The particles that are detected are smaller than the soot size range and do not occur in greater numbers than those from a diesel engine in the corresponding size range.

Combustion information from three combustion chamber geometries was analyzed: Pancake and horseshoe geometry on a single-cylinder research engine, and pentroof geometry in a turbocharged four-cylinder production engine. Four different fuels were used. In the horseshoe configuration, the cylinder pressure traces from the burnt gas and from the end-gas pocket were evaluated. It is shown that the characteristics of knock are to a large degree a function of the combustion chamber geometry and that they are influenced strongly by the transducer position. It is shown for pentroof geometry that the number of cycles required to properly describe the knock population is a function of the knock intensity. A large error potential is shown for samples smaller than about 100 - 200 consecutive cycles. Good agreement between knock description based on accelerometer data and based on pressure data was found.

The purpose of this work was to investigate the influence of fuel parameters on emissions, combustion and cycle to cycle IMEP variations in a single cylinder version of a commercial direct injection stratified charge (DISC) spark ignition engine. The emission measurements employed both conventional emission measurement equipment as well as on-line gas chromatography/mass spectrometry (GC/MS). Four different fuels were compared in the study. The fuel parameters that were studied were distillation range and MTBE (Methyl Tert Buthyl Ether) content. A European certification gasoline fuel was used as a reference. The three other fuels contained 10% MTBE. The measurements were performed at a low engine speed and at a low, constant load. The engine was operated in stratified mode. The start of injection was altered 15 crankangle degrees before and after series calibration with fixed ignition timing in order to vary mixture preparation time.