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Alcohol-based fuels are a viable alternative to fossil fuels for powering vehicles. As a drop-in fuel, an oxygenated fuel blend containing the C8 alcohol 2-ethylhexanol (isomer of octanol), hydrotreated vegetable oil (HVO) and rapeseed methyl ester (RME) can reduce soot and NOx emissions whilst maintaining engine performance. However, fuel injection strategy significantly affects combustion and hence has been investigated with a view to reducing emissions whilst maintaining engine efficiency. In a single cylinder light-duty compression ignition research engine, the effect of different injection strategies (main, main/post, double pre/main, double pre/main/post injection) and EGR levels (0%, 19%) on specifically NOx, soot emissions and particle size distribution was investigated for three different fuels: fossil diesel fuel, HVO and the oxygenated blend. The blend was designed to have diesel-like combustion properties (cetane number of 52) and had an oxygen content of 5.4% by mass.

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.

Future demands for improvements in the fuel economy of gasoline passenger car engines will require the development and implementation of advanced combustion strategies, to replace, or combine with the conventional spark ignition strategy. One possible strategy is homogeneous charge compression ignition (HCCI) achieved using negative valve overlap (NVO). However, several issues need to be addressed before this combustion strategy can be fully implemented in a production vehicle, one being to increase the upper load limit. One constraint at high loads is the combustion becoming too rapid, leading to excessive pressure-rise rates and large pressure fluctuations (ringing), causing noise. In this work, efforts were made to reduce these pressure fluctuations by using a late injection during the later part of the compression. A more appropriate acronym than HCCI for such combustion is SCCI (Stratified Charge Compression Ignition).

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.

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.

A single-cylinder engine was operated in HCCI combustion mode with different kinds of commercial fuels. The HCCI combustion was generated by creating a negative valve overlap (early exhaust valve closing combined with late intake valve opening) thus trapping a large amount of residuals (∼ 55%). Fifteen different fuels with high octane numbers were tested six of which were primary reference fuels (PRF's) and nine were commercial fuels or reference fuels. The engine was operated at constant operational parameters (speed/load, valve timing and equivalence ratio, intake air temperature, compression ratio, etc.) changing only the fuel type while the engine was running. Changing the fuel affected the auto-ignition timing, represented by the 50% mass fraction burned location (CA50). However these changes were not consistent with the classical RON and MON numbers, which are measures of the knock resistance of the fuel. Indeed, no correlation was found between CA50 and the RON or MON numbers.

The possibilities of operating a direct injection Diesel engine in HCCI combustion mode with early injection of conventional Diesel fuel were investigated. In order to properly phase the combustion process in the cycle and to prevent knock, the geometric compression ratio was reduced from 17.0:1 to 13.4:1 or 11.5:1. Further control of the phasing and combustion rate was achieved with high rates of cooled EGR. The engine used for the experiments was a single cylinder version of a modern passenger car type common rail engine with a displacement of 480 cc. An injector with a small included angle was used to prevent interaction of the spray and the cylinder liner. In order to create a homogeneous mixture, the fuel was injected by multiple short injections during the compression stroke. The low knock resistance of the Diesel fuel limited the operating conditions to low loads. Compared to conventional Diesel combustion, the NOx emissions were dramatically reduced.

Heat transfer to the walls of the combustion chamber is increased by engine knock. In this study the influence of knock onset and knock intensity on the heat flux is investigated by examining over 10 000 individual engine cycles with a varying degree of knock. The heat transfer to the walls was estimated by measuring the combustion chamber wall temperature in an SI engine under knocking conditions. The influence of the air-fuel ratio and the orientation of the oscillating cylinder pressure-relative to the combustion chamber wall-were also investigated. It was found that knock intensities above 0.2 Mpa influenced the heat flux. At knock intensities above 0.6 Mpa, the peak heat flux was 2.5 times higher than for a non-knocking cycle. The direction of the oscillations did not affect the heat transfer.

SI Engine knock is caused by autoignition in the unburnt part of the mixture (end-gas) ahead of the propagating flame. Autoignition of the end-gas occurs when the temperature and pressure exceeds a critical limit when comparatively slow reactions-releasing moderate amounts of heat-transform into ignition and rapid heat release. In this paper the difference in the heat released in the end-gas-by low temperature chemistry-between lean, rich, stochiometric, and stoichiometric mixtures diluted with cooled EGR was examined by measuring the temperature in the end-gas with Dual Broadband Rotational CARS. The measured temperature history was compared with an isentropic temperature calculated from the cylinder pressure trace. The experimentally obtained values for knock onset were compared with results from a two-zone thermodynamic model including detailed chemistry modeling of the end-gas reactions.

A single cylinder, naturally aspirated, four-stroke and camless (Otto) engine was operated in homogeneous charge compression ignition (HCCI) mode with commercial gasoline. The valve timing could be adjusted during engine operation, which made it possible to optimize the HCCI engine operation for different speed and load points in the part-load regime of a 5-cylinder 2.4 liter engine. Several tests were made with differing combinations of speed and load conditions, while varying the valve timing and the inlet manifold air pressure. Starting with conventional SI combustion, the negative valve overlap was increased until HCCI combustion was obtained. Then the influences of the equivalence ratio and the exhaust valve opening were investigated. With the engine operating on HCCI combustion, unthrottled and without preheating, the exhaust valve opening, the exhaust valve closing and the intake valve closing were optimized next.

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 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).

A literature survey was carried out to examine the advances in knowledge regarding spray impingement on surfaces over the last five years. Published experiments indicate that spray impingement is controlled by various spray parameters, surface conditions, and liquid properties. One disadvantage of the published results is that the experiments have mainly been conducted with water droplets or diesel fuel, often at atmospheric conditions. A sensitivity analysis was performed for one common impingement model. The purpose was to investigate how the model described different phenomena when different parameters were changed, including wall temperature, wall roughness and injection velocity of the spray. The model tested showed sensitivity to surface roughness, whereas changes in wall temperature only resulted in increased evaporation from the surface. The increase of injection velocity resulted in a decrease of fuel on the wall by 70%.

It is generally accepted that knocking combustion influences the heat transfer in SI engines. However, the effects of heat transfer on the onset of knock is still not clear due to lack of experimental data of the thermal boundary layer close to the combustion chamber wall. This paper presents measurements of the temperature in the thermal boundary layer under knocking and non-knocking conditions. The temperature was measured using dual-broadband rotational Coherent anti-Stokes Raman Spectroscopy (CARS). Simultaneous time-resolved measurements of the cylinder pressure, at three different locations, and the heat flux to the wall were carried out. Optical access to the region near the combustion chamber wall was achieved by using a horseshoe-shaped combustion chamber with windows installed in the rectangular part of the chamber. This arrangement made CARS temperature measurements close to the wall possible and results are presented in the range 0.1-5 mm from the wall.

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.

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.

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.

A system for stratifying recycled exhaust gas (EGR) in order to substantially increase dilution tolerance has been applied to a single cylinder manifold injected pent-roof four-valve gasoline engine. This system has been given the generic name Combustion Control by Vortex Stratification (CCVS). Preliminary research has shown that greatly improved fuel consumption is achievable at stoichiometric conditions compared to a conventional version of the same engine whilst retaining ULEV NOx levels. Simultaneously the combustion system has shown inherently low HC emissions compared to homogeneous EGR engines. A production viable variable air motion system has also been assessed which increases the effectiveness of the stratification whilst allowing full load refinement and retaining high performance.