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The autoignition resistance of a practical gasoline is best characterized by the Octane Index, OI, defined as RON-KS, where RON and MON are respectively, Research and Motor Octane Numbers, S is the sensitivity (RON-MON) and K is a constant depending on the pressure and temperature history of the fuel/air mixture in an engine. Experiments in knocking SI engines, HCCI engines and in premixed compression ignition (PCI) engines have shown that if two fuels of different composition have the same OI and experience the same pressure/temperature history, they will have the same autoignition phasing. A practical gasoline is a complex mixture of hydrocarbons and a simple surrogate is needed to describe its autoignition chemistry. A mixture of toluene and PRF (iso-octane + n-heptane), TPRF, can have the same RON and S as a target gasoline and so will have the same OI at any given K value and will be a very good surrogate for the gasoline.

Compared to conventional diesel combustion (CDC), isobaric combustion can achieve a similar or higher indicated efficiency, lower heat transfer losses, reduced nitrogen oxides (NOx) emissions; however, with a penalty of soot emissions. While the engine performance and exhaust emissions of isobaric combustion are well known, the overall flame development, in particular, the flow-field details within the flames are unclear. In this study, the performance analysis of CDC and two isobaric combustion cases was conducted, followed by high-speed imaging of Mie-scattering and soot luminosity in an optically accessible, single-cylinder heavy-duty diesel engine. From the soot luminosity imaging, qualitative flow-fields were obtained using flame image velocimetry (FIV). The peak motoring pressure (PMP) and peak cylinder pressure (PCP) of CDC are kept fixed at 50 and 70 bar, respectively.

Pre-chamber combustion (PCC) allows an extension on the lean limit of an internal combustion engine (ICE). This combustion mode provides lower NOx emissions and shorter combustion durations that lead to a higher indicated efficiency. In the present work, a narrow throat pre-chamber was tested, which has a unique nozzle area distribution in two rows of six nozzle holes each. Tests were carried out in a modified heavy-duty engine for optical visualization. Methane was used as fuel for both the pre-chamber and the main chamber. Seven operating points were tested, including passive pre-chamber mode as a limit condition, to study the effect of pre- and main-chamber fuel addition on the pre-chamber jets and the main chamber combustion via chemiluminescence imaging. A typical cycle of one of the tested conditions is explained through the captured images. Observations of the typical cycle reveal a predominant presence of only six jets (from the lower row), with well-defined jet structures.

The regulatory requirements to reduce both greenhouse gases and exhaust gas pollutants from heavy duty engines are driving new perspectives on the interaction between fuels and engines. Fuels that reliefs the burden on engine manufacturers to reach these goals are of particular interest. A low carbon fuel with a higher volatility and heating value than diesel is one such fuel that reduces engine-out emissions and carbon footprint from the entire hydrocarbon lifecycle (well-to-wheel) and improves fuel efficiency, which is a main enabler for gasoline compression ignition (GCI) technology. The present study investigated the potential of GCI technology by evaluating the performance of a low carbon high efficiency, high reactivity gasoline fuel in Doosan’s 6L medium duty diesel engine.

The current trend toward more fuel efficient vehicles with lower emission levels has prompted development of new combustion techniques for use in gasoline engines. Stratified combustion has been shown to be a promising approach for increasing the fuel efficiency. However, this technique is hampered by drawbacks such as increased particulate and standard emissions. This study attempts to address the issues of increased emission levels by investigating the influence of high frequency ionizing ignition systems, 350 bar fuel injection pressure and various tumble levels on particulate emissions and combustion characteristics in an optical SGDI engine operated in stratified mode on isooctane. Tests were performed at one engine load of 2.63 bar BMEP and speed of 1200 rpm. Combustion was recorded with two high speed color cameras from bottom and side views using optical filters for OH and soot luminescence.

The potential of 48V Mild Hybrid is promising in meeting the present and future CO2 legislations. There are various system layouts for 48V hybrid system including P0, P1, P2. In this paper, P2 architecture is used to investigate the effects of water injection benefits in a mild hybrid system. Electrification of the conventional powertrain uses the benefits of an electric drive in the low load-low speed region where the conventional SI engine is least efficient and as the load demand increases the IC Engine is used in its more efficient operating region. Engine downsizing and forced induction trend is popular in the hybrid system architecture. However, the engine efficiency is limited by combustion knocking at higher loads thus ignition retard is used to avoid knocking and fuel enrichment becomes must to operate the engine at MBT (Maximum Brake Torque) timing; in turn neutralizing the benefits of fuel savings by electrification.

The present investigation expands on our previous work on development of fast idle catalyst light-off strategy for a light duty gasoline compression ignition (GCI) engine. In part 1, the steady state experimental investigation in a single cylinder GCI engine indicate an optimum strategy for effective catalyst light off during cold start fast idle operation. According to this strategy, the strategy includes (1) dispersing a first fuel injection during the intake stroke, (2) dispersing a second fuel injection during the expansion stroke, and (3) igniting a spark during the expansion stroke. This strategy increases the exhaust temperature during cold starts thereby assisting in lighting the oxidation catalyst, and reduce emissions and provide greater combustion stability as compared to other injection and spark strategies.

The present investigation pertains to the development of fast idle catalyst light-off strategy for a light duty gasoline compression ignition (GCI) engine. The engine cold start fast idle operation poses a problem of increased criteria emissions if the catalyst is not activated during the warm up period. Therefore, a control strategy is proposed here to minimize the criteria pollutants during the fast idle phase via enabling fast catalyst light off in a GCI engine and relying on the spark ignition of a globally stoichiometric fuel air mixture. The engine has unique design features such as certain geometry configuration between spark plug and fuel injector arrangement, and the location of spark plug in a high compression ratio (CR) diesel-like combustion chamber. The experiments were performed in a single cylinder GCI engine at cold start fast idle conditions using certification gasoline fuel (RON 91).

Gasoline compression ignition (GCI) technology shows the potential to obtain high thermal efficiencies while maintaining low soot and NOx emissions in light-duty engine applications. Recent experimental studies and numerical simulations have indicated that high reactivity gasoline-like fuels can further enable the benefits of GCI combustion. However, there is limited empirical data in the literature studying the gasoline compression ignition process at relevant in-cylinder conditions, which are required for further optimizing combustion system designs. This study investigates the temporal and spatial evolution of the compression ignition process of various high reactivity gasoline fuels with research octane numbers (RON) of 71, 74 and 82, as well as a conventional RON 97 E10 gasoline fuel. A ten-hole prototype gasoline injector specifically designed for GCI applications capable of injection pressures up to 450 bar was used.

Drag reducing agents (DRAs) are extensively used to increase the capacity of pipelines to transport crude oils and finished products. The amount of DRA that can be used in gasoline is limited by the tendency of the high molecular weight DRAs to form engine deposits. The use of deposit control additives (DCAs) could help to mitigate this effect, enabling increased DRA treatment rates and improved pipeline capacity. A study has been undertaken to investigate the engine test response of these additives, and has suggested that higher DRA treat rates may be possible when accompanied by a deposit control additive to address increased intake valve deposits. Conversely, the effect on combustion chamber deposits is not clear and further studies would be required. Other engine related aspects such as intake valve deposit stick have also been investigated and under the conditions tested do not appear to be adversely affected by either the DRA or the deposit control additive.

The interaction between a combusting diesel spray and a wall was studied by measuring the spray flame temperature time and spatially resolved. The influence of injection sequences, injection pressure and gas conditions on the heat transfer between the combusting spray and the wall was investigated by measuring the flame temperature during the complete injection event. The flame temperature was measured by an emission based optical method and determined by comparing the relative emission intensities from the soot in the flame at two wavelength intervals. The measurements were done by employing a monochromatic and non intensified high speed camera, an array of mirrors, interference filters and a beam splitter. The studies were carried out in the Chalmers High Pressure High Temperature (HP/HT) spray rig at conditions similar to those prevailing in a direct injected diesel engine prior to the injection of fuel.

In the context of stringent future emission standards as well as the need to reduce emissions of CO2 on a global scale, the cost of manufacturing engines is increasing. Naphtha has been shown to have beneficial properties for its use as a fuel in the transportation sector. Well to tank CO2 emissions from the production of Naphtha are lower than any other fuel produced in the refinery due to its lower processing requisites. Moreover, under current technology trends the demand for diesel is expected to increase leading to a possible surplus of light fuels in the future. Recent research has demonstrated that significant fuel consumption reduction is possible based on a direct injection gasoline engine system, when a low quality gasoline stream such as Naphtha is used in compression ignition mode. With this fuel, the engine will be at least as efficient and clean as current diesel engines but will be more cost effective (lower injection pressure, HC/CO after-treatment rather than NOx).

High-pressure isobaric combustion used in the double compression expansion engine (DCEE) concept was proposed to obtain higher engine brake thermal efficiency than the conventional diesel engine. Experiments on the metal engines showed that four consecutive injections delivered by a single injector can achieve isobaric combustion. Improved understanding of the detailed fuel-air mixing with multiple consecutive injections is needed to optimize the isobaric combustion and reduce engine emissions. In this study, we explored the fuel spray characteristics of the four-consecutive-injections strategy using high-speed imaging with background illumination and fuel-tracer planar laser-induced fluorescence (PLIF) imaging in a heavy-duty optical engine under non-reactive conditions. Toluene of 2% by volume was added to the n-heptane and served as the tracer. The fourth harmonic of a 10 Hz Nd:YAG laser was applied for the excitation of toluene.

A series of experimental studies of diesel spray combustion was carried out using non-circular and back-step orifices. The experiments were performed in a single-cylinder engine and in a constant volume combustion chamber. In the engine tests, elliptic orifices with an aspect ratio of approximately 2:1 were compared with circular orifices. The elliptic orifices had sharp inlets and the circular orifices had rounded inlets. Elliptic orifices aligned with either the minor axis or the major axis in the direction of the nozzle tip were tested. The orifice shapes had minor effects on the heat release, ignition delay, and emissions of smoke, CO and HC. However, substantial differences were observed for emissions of NOx: for the vertical elliptic orifices, emissions up to 37.6 percent lower than with circular orifices were observed. In the combustion bomb tests, rectangular and back-step orifices were compared with circular orifices, all with sharp inlets.

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.

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.

The effects of multiple injections on engine-out emissions from a high-speed direct injection (HSDI) diesel engine were investigated in a series of experiments using a single cylinder research engine. Injection sequences in which the main injection was split into two, three and four pulses were tested and the resulting emissions (NOx, CO HC and particulate matter), torque and cylinder pressures were compared to those obtained with single injections. Together with the number of injections, the effects of varying the dwell time were also investigated. It was found that dividing the main injection into two parts lowered the engine-out particulate and CO emissions and increased fuel efficiency. However, it also resulted in increased NOx emissions.

A Turbulent Flame Speed Closure Model is modified and implemented into the FIRE code for use in 3D computations of combustion in an SI-engine. The modifications are done to account for mixture inhomogeneity, and mixture compression through the dependency of local equivalence ratio, pressure and temperature on the chemical time scale and a global reaction time scale. The model is also subjected to further evaluation against experimental data, covering different mixture and turbulence conditions. The combustion process in a 4-valve pentroof combustion chamber is simulated and heat release rates and spatial flame distribution are evaluated against experimental data. The computations show good agreement with the experiments. The model has proven to be a robust and time effective simulation tool with good predictive ability.

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).