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The influence of ethanol content in gasoline on speciated emissions from a direct injection stratified charge (DISC) SI engine is assessed. The engine tested is a commercial DISC one that has a wall guided combustion system. The emissions were analyzed using both Fourier transform infrared (FTIR) spectroscopy and conventional emission measurement equipment. Seven fuels were compared in the study. The first range of fuels was of alkylate type, designed to have 0, 5, 10 and 15 % ethanol in gasoline without changing the evaporation curve. European emissions certification fuel was tested, with and without 5 % ethanol, and finally a specially blended high volatility gasoline was also tested. The measurements were conducted at part-load, where the combustion is in stratified mode. The engine used a series engine control unit (ECU) that regulated the fuel injection, ignition and exhaust gas recirculation (EGR).

This work investigates the influence of fuel parameters on deposit formation and emissions in a four-cylinder direct injection stratified charge (DISC) SI engine. The engine tested is a commercial DISC engine with a wall-guided combustion system. The combustion chamber deposits (CCDs) were analyzed with gas chromatography / mass spectrometry as well as thickness and mass measurements. Intake valve deposits (IVDs) were analyzed for mass, while internal injector deposits were evaluated using spray photography. The CCD build-up was obtained with the CEC1 F-020-A-98 performance test for evaluation of the influence of fuels and additives on IVDs and CCDs in port fuel injected SI engines. The 60 h test is designed to simulate city driving. Four fuels were compared in the study: a base gasoline, with and without a fuel additive, a specially blended high volatility gasoline, and a fuel representing the worst case of European gasolines; neither of the latter two had additives.

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.

Interest in spray-wall interactions has grown because of the development of direct-injection stratified-charge (DISC) spark ignition (SI) engines. In this type of engine, impingement of the spray on the piston wall often leads to high emissions of unburned hydrocarbons and soot. These emissions have proven to be one of the major drawbacks of the DISC SI engine, so it is important to obtain detailed knowledge about the different processes involved in spray impingement and their effects. In this study, the size and velocity of droplets reflected from a wall were characterized by Phase Doppler Anemometry (PDA). The impinging spray was also visualized using an AVL VisioScope. The experiments were carried out on a real gasoline spray impinging on a wall under simulated engine conditions in a spray chamber. A sensitivity analysis was carried out to investigate the influence of different wall properties and wall temperature, on the impingement and secondary atomization processes.

Ion current sensors have high potential utility for obtaining feedback signals directly from the combustion chamber in internal combustion engines. This paper describes experiments performed in a single-cylinder optical engine operated in HCCI mode with negative valve overlap to explore this potential. A high-speed CCD camera was used to visualize the combustion progress in the cylinder, and the photographs obtained were compared with the ion current signals. The optical data indicate that the ions responsible for the chemiluminescence from the HCCI combustion have to be in contact with the sensing electrode for an ion current to start flowing through the measurement circuit. This also means that there will be an offset between the time at which 50% of the fuel mass has burned and 50% of the ion current peak value is reached, which is readily explained by the results presented in the paper.

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.

To elucidate the processes controlling the auto-ignition timing and overall combustion duration in homogeneous charge compression ignition (HCCI) engines, the distribution of the auto-ignition sites, in both space and time, was studied. The auto-ignition locations were investigated using optical diagnosis of HCCI combustion, based on laser induced fluorescence (LIF) measurements of formaldehyde in an optical engine with fully variable valve actuation. This engine was operated in two different modes of HCCI. In the first, auto-ignition temperatures were reached by heating the inlet air, while in the second, residual mass from the previous combustion cycle was trapped using a negative valve overlap. The fuel was introduced directly into the combustion chamber in both approaches. To complement these experiments, 3-D numerical modeling of the gas exchange and compression stroke events was done for both HCCI-generating approaches.

The objective of the study presented here was to examine the possibility of simultaneously reducing soot and nitrogen oxide (NOx) emissions from a heavy duty diesel engine, using very high levels of EGR (exhaust gas recirculation). The investigation was carried out using a 2 litre DI single cylinder diesel engine. Two different EGR strategies were examined. One entailed maintaining a constant charge air pressure with a varied exhaust back pressure in order to change the amount of EGR. In the other strategy a constant pressure difference was maintained over the engine, resulting in different equivalence ratios at similar EGR levels. EGR levels of 60 % or more significantly reduced both soot and NOx emissions at 25 % engine load with constant charge air pressure and increasing exhaust back pressure. However, combustion under these conditions was incomplete, resulting in high emissions of carbon monoxide (CO), unburned hydrocarbons (HC) and high fuel consumption.

The possibilities for extending the range of engine loads in which soot and NOx emissions can be minimised by using low temperature combustion in conjunction with high levels of EGR was investigated in a series of experiments with a single cylinder research engine. The results show that very low levels of both soot and NOx emissions can be achieved at engine loads up to 50 % by reducing the compression ratio to 14 and applying high levels of EGR (up to approximately 60 %). Unfortunately, the low temperature combustion is accompanied by increases in fuel consumption and emissions of both HC and CO. However, these drawbacks can be reduced by advancing the injection timing. The research engine was a 2 litre direct injected (DI), supercharged, heavy duty, single cylinder diesel engine with a geometry based on Volvo's 12 litre engine, and the amount of EGR was increased by adjusting the exhaust back pressure while keeping the charge air pressure constant.

Fuel wetting in the inlet port of a gasoline engine was studied using Laser-Induced Fluorescence (LIF). The measurements were done directly on the metal wall surface. Quantitative results were be obtained using a special calibration procedure. The sensitivity of the technique was found to correspond to a fuel layer thickness in the order of 1 μm, and the accuracy was estimated to be approx. 10 %. The engine was run on iso-octane, and in order to obtain fluorescence a dopant (3-pentanone) was added to the fuel. Laser light with a wave length of 266 nm was generated by frequency doubling the light from a Nd-YAG laser in two steps. A laser sheet was directed into the intake port and the fuel layer on the wall could be studied along a line on the bifurcation wall. The fluorescence light was detected with an intensified diode-array camera. The measurements from the fuel film thickness were compared with measurements of the total fuel film mass using an A/F response method.

In this study, the effects of varying the start of injection in a Free Piston Engine (FPE) have been investigated, using the KIVA-3V CFD code. In order to simulate the FPE the code has been modified by replacing the conventional crank shaft controlled piston motion by a piston motion profile calculated using a MATLAB/SIMULINK model. In this model, the piston motion is controlled by Newton's second law and the combustion process is represented by a simplified model based on ignition delay integrals and Wiebe functions. The results were tuned using predictions from the SENKIN software which are based on the detailed chemical kinetics mechanism of a Diesel oil surrogate represented by a blend of the main aliphatic (70% n-heptane) and aromatic (30% toluene) components. In order to help analyze the emission formation resulting from the HCCI/PPCI combustion modes in the engine, a special approach based on the temperature-equivalence ratio maps has been developed.

When using dimethyl ether (DME) to fuel diesel engines at high load and speed, applying high amounts of exhaust gas recirculation (EGR) to limit NOX emissions, carbon monoxide (CO) emissions are generally high. To address this issue, the combustion and emission processes in such engines were analyzed with the three-dimensional CFD KIVA3V code. The combustion sub-mechanism (76 species and 375 reactions) was validated by comparing simulated ignition delays and flame velocities to reference data under diesel-like and atmospheric conditions, respectively. In addition, simulated and experimentally determined rate of heat release (RoHR) curves and emission data were compared for a heavy-duty single-cylinder DME engine (displaced volume, 2.02 liters) with DME-adapted piston and nozzle geometries. The simulated RoHR curves captured the main features of the experimentally measured curves, but deviated in the premixed (higher peak) and late combustion phases (too high).

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.

An experimental investigation was carried out in which an HSDI Common Rail Diesel engine was operated in both HCCI and conventional Diesel combustion modes, using conventional Diesel fuel in both cases. The engine used in the experiments was a single cylinder version of a modern passenger car engine with a displacement of 480 cc. In HCCI mode, the fuel was injected in multiple stages during the compression stroke, using a nozzle with a 60° included angle. To control the phasing and rate of combustion, the effective compression ratio was reduced by retarded intake valve closing. In addition, increased amounts of EGR were used. HCCI operation reduced soot and NOx emissions significantly. The use of a narrow included angle for conventional Diesel operation increased emissions significantly. The effect of a wider included angle and modifications to the piston were investigated experimentally and numerically.

The effects of using n-butanol, n-octanol, fossil Diesel, hydrotreated vegetable oil (HVO), and blends of these fuels on spray penetration, flame and soot characteristics were investigated in a high-pressure high-temperature constant volume combustion chamber designed to mimic a heavy duty Diesel engine. Backlight illumination was used to capture liquid and vapor phase spray images with a high-speed camera. The flame lift-off length (LOL) and ignition delay were determined by analyzing OH* chemiluminescence images. Laser extinction diagnostics were used to measure the spatially and temporally resolved soot volume fraction. The spray experiments were performed by injecting fuels under non-combusting (623 K) and combusting (823 K) conditions at a fixed ambient air density of 26 kg/m3. A Scania 0.19 mm single straight hole injector and Scania XPI common rail fuel supply system were used to produce injection pressures of 120 MPa and 180 MPa.

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.

The effects of using an SI stratified charge in combination with HCCI combustion on combustion phasing, rate of heat release and emissions were investigated in engine experiments to identify ways to extend the operational range of HCCI combustion to lower loads. In the experiments an optical single-cylinder engine equipped with a piezo electric outward-opening injector and operated with negative valve overlap (NVO) and low lift, short duration, camshaft profiles, was used to initiate HCCI combustion by increasing the exhaust gas recirculation (EGR) and thus retaining sufficient thermal energy to reach auto-ignition temperatures. Two series of experiments with full factorial designs were performed, to investigate how the tested parameters (amounts of fuel injected in pilot injections and main injections, stratification injection timing and spark-assistance) influenced the combustion.

A regular flex-fuel engine can operate on any blend of fuel between pure gasoline and E85. Flex-fuel engines have relatively low efficiency on E85 because the hardware is optimized for gasoline. If instead the engine is optimized for neat ethanol, the efficiency may be much higher, as demonstrated in this paper. The studied two-liter engine was modified with a much higher compression ratio than suitable for gasoline, two-stage turbocharging and direct injection with piezo-actuated outwards-opening injectors, a stratified combustion system and custom in-house control system. The research engine exhibited a wide-open throttle performance similar to that of a naturally aspirated v8, while offering a part-load efficiency comparable to a state-of-the-art two-liter naturally aspirated engine. NOx will be handled by a lean NOx trap. Combustion characteristics were compared between gasoline and neat ethanol.

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.

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.