Search Results

This paper investigates the application of a Bottoming Cycle (BC) applied to a 10-litre (L) heavy duty Diesel engine for potential improvements in fuel efficiency. With the main thermodynamic irreversibility in the BC due to the temperature difference between the heat source and the working fluid, a proper selection of the working fluid and its operating condition for a given waste heat is the key in achieving high overall conversion efficiency. The paper reviews a fluid selection methodology based on thermodynamic/thermo-physical and environmental/safety properties. Results are presented using seven pure, dry, isentropic and wet working fluids (synthetic, organic and inorganic) operating with expansion starting from the saturated vapour, superheated vapour, supercritical phase, saturated liquid, and two-phase. Efficiency improvements by recovering Charge Air Coolers (CAC) and Exhaust Gas Recirculation (EGR) cooler heat on two engine platforms were calculated.

A multi-cycle three-dimensional CFD engine simulation programme has been developed and applied to analyze the Controlled autoignition (CAI) combustion, also known as homogeneous charge compression ignition (HCCI), in a direct injection gasoline engine. CAI operation was achieved through the negative valve overlap method by means of a set of low lift camshafts. The effect of single injection timing on combustion phasing and underlying physical and chemical processes involved was examined through a series of analytical studies using the multi-cycle 3D engine simulation programme. The analyses showed that early injection into the trapped burned gases of a lean-burn mixture during the negative valve overlap period had a large effect on combustion phasing, due to localized heat release and the production of chemically reactive species. As the injection was retarded to the intake stroke, the charge cooling effect tended to slow down the autoignition process.

An experimental study of the mixture response performance of novel, port-fuel injection strategies upon combustion stability in a gasoline engine was undertaken at low engine load and speed conditions in the range of 1.0 bar to 1.8 bar GIMEP and 1000 rpm to 1800 rpm. The aim was to improve the thermal efficiency of the engine, by extending the lean limit of combustion stability, through promotion of stable charge stratification. The investigation was carried out using a modified 4-valve single-cylinder head, derived from a 4-cylinder, pent-roof, production, gasoline engine. The cylinder head was modified by dividing the intake tract into two, separate and isolated passages; each incorporating a production fuel injector. The fuel injection timing and duration were controlled independently for each injector.

The research presented here aims at providing a deeper understanding of the formation of nitric oxide in diesel combustion. To this end, in-cylinder distributions of nitric oxide (NO) were acquired by laser-induced fluorescence (LIF) in a rapid compression machine at conditions representative of a modern diesel passenger vehicle. In particular, the effects of injection and in-cylinder pressure on NO formation were investigated temporally and spatially to offer new insight into the formation of NO. Excitation and collection strategies were notably fine-tuned to avoid the collection of spurious signal due to oxygen (O₂) fluorescence. NO fluorescence was first recorded slightly after the onset of the diffusion flame and until late in the expansion stroke. The early low levels of NO were located on the lean side of the high density of hydroxyl radicals (OH).

The influences of injector nozzle geometry, injection pressure and ambient air conditions on a diesel fuel spray were examined using back-lighting techniques. Both stills and high speed imaging techniques were used. Operating conditions representative of a modern turbocharged aftercooled HSDI diesel engine were achieved in an optical rapid compression machine fitted with a common rail fuel injector. Qualitative differences in spray structure were observed between tests performed with short and long injection periods. Changes in the flow structure within the nozzle could be the source of this effect. The temporal liquid penetration lengths were derived from the high-speed images. Comparisons were made between different nozzle geometries and different injection pressures. Differences were observed between VCO (Valve Covers Orifice) and mini-sac nozzles, with the mini-sac nozzles showing a higher rate of penetration under the same conditions.

For optimum efficiency, the direct injection (DI) gasoline engine requires two operating modes to cover the full load/speed map. For lower loads and speeds, stratified charge operation can be used, while homogeneous charge is required for high loads and speeds. This paper has focused its attention on the latter of these modes, where the performance is highly dependent on the quality of the fuel spray, evaporation and the air-fuel mixture preparation. Results of quantitative and qualitative Laser Induced Fluorescence (LIF) measurements are presented, together with shadow-graph spray imaging, made within an optically accessed DI gasoline engine. These are compared with previously acquired air flow measurements, at various injection timings, and with engine performance and emissions data obtained in a fired single cylinder non-optical engine, having an identical cylinder head and piston crown geometry.

The application of controlled auto-ignition (CAI) combustion in gasoline direct injection (GDI) engines is becoming of more interest due to its great potential of reducing both NOx emissions and fuel consumption. Injection timing has been known as an important parameter to control CAI combustion process. In this paper, the effect of injection timing on mixture and CAI combustion is investigated in a single-cylinder GDI engine with an air-assisted injector. The liquid and vapour phases of fuel spray were measured using planar laser induced exciplex fluorescence (PLIEF) technique. The result shows that early injection led to homogeneous mixture but late injection resulted in serious stratification at the end of compression. CAI combustion in this study was realized by using short-duration camshafts and early closure of the exhaust valves. During tests, the engine speed was varied from 1200rpm to 2400rpm and A/F ratio from stoichiometric to lean limit.

The automobile industry is under intense pressure to reduce carbon dioxide (CO2) emissions of vehicles. There is also increasing pressure to reduce the other tail-pipe emissions from vehicles to combat air pollution. Electric powertrains offer great potential for eliminating tailpipe CO2 and all other tailpipe emissions. However, current battery technology and recharging infrastructure still present limitations for some applications, where a continuous high-power demand is required. Furthermore, not all markets have the infrastructure to support a sizeable electric fleet and until the grid energy generation mix is of a sufficiently low carbon intensity, then significant vehicle life-cycle CO2 savings could not be realized by the Battery Electric Vehicles. This investigation examines the effects of combustion, efficiencies, and emissions of two alcohol fuels that could help to significantly reduce CO2 in both tailpipe and the whole life cycle.

This paper presents the simulation study on the effects of mechanical turbo-compounding on a turbocharged diesel engine. A downstream power-turbine has been coupled to the exhaust manifold after the main turbocharger, in the aim to recover waste heat energy. The engine in the current study is Scania DC13-06, which 6 cylinders and 13 litre in capacity. The possibilities, effectiveness and working range of the turbo compounded system were analyzed in this study. The system was modeled in AVL BOOST, which is a one dimensional (1D) engine code. The current study found that turbo compounding could possibly recover on average 11.4% more exhaust energy or extra 3.7kW of power. If the system is mechanically coupled to the engine, it could increase the average engine power by up to 1.2% and improve average BSFC by 1.9%.

The Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI) can be achieved by the negative valve overlap method in conjunction with direct injection in a four-stroke gasoline engine. A multi-cycle 3D engine simulation program has been developed and applied to study the effect of injection timing on CAI operations with lean and stoichiometric mixtures. The combustion models used in the present study are based on the modified Shell auto-ignition model and the characteristic-time combustion model. A liquid sheet breakup spray model was used for the droplet breakup processes. Based on the parametric studies on injection timing and equivalence ratio, the major difference between stoichiometric and lean-burn CAI operations is due to the fact that fuel injections take place during the negative valve overlap period.

Having achieved CAI-combustion in a 4-cylinder four-stroke gasoline DI engine the effects of ignition timing on the CAI combustion process were investigated through the introduction of spark. By varying the start of fuel injection, the effects on Indicated Specific values for NOx, HC, CO emissions and fuel consumption were investigated for CAI combustion. The CAI combustion process was then assisted by spark and three different ignition timings were studied. The effect on engine performance and the emission specific values were investigated further. The engine speed was maintained at 1500 rpm and lambda was kept constant at 1.2. It was found that with spark-assisted CAI, IMEP and ISNOx values increased as compared with typical CAI. ISHC values were lower for spark-assisted CAI as compared to typical CAI. Heat release data was studied to better understand this phenomenon.

The pursuit of flexibility is a recurring theme in engine design and development. Engines that are able to switch between the two-stroke operating cycle and four-stroke operation promise a great leap in flexibility. Such 2S-4S engines could then continuously select the optimum operating mode - including HCCI/CAI combustion - for fuel efficiency, emissions or specific output. With recent developments in valvetrain technology, advanced boosting devices, direct fuel injection and engine control, the 2S-4S engine is an increasingly real prospect. The authors have undertaken a comprehensive feasibility study for 2S-4S gasoline engines. This study has encompassed concept and detailed design, design analysis, one-dimensional gas dynamics simulation, three-dimensional computational fluid dynamics, and vehicle simulation. The resulting 2/4SIGHT concept engine is a 1.04 l in-line three-cylinder engine producing 230 Nm and 85 kW.

Two optical techniques together with a CFD simulation have been used to study the interaction of intake airflow with the injected fuel spray in a motored direct injection gasoline engine. The combustion chamber was of a pent-roof construction with the side-mounted injector located low down between the inlet valves injecting at a 54° angle to the cylinder axis. The two-dimensional piston bowl shape allowed optical access for the Mie scatter technique to be used to investigate the liquid fuel behaviour in the central axial plane of the cylinder lying midway between the two inlet valves and passing through the centre line of the injector nozzle. A second set of images was obtained using backlighting, this time looking through the glass cylinder liner directly towards the injector. The in-cylinder simulation was run using the VECTIS software. Measurements and simulations were conducted for a range of early SOI timings between 20° and 80° ATDC.

The Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI) was achieved by trapping residuals with early exhaust valve closure in conjunction with direct injection. Multi-cycle 3D engine simulations have been carried out for parametric study on four different injection timings, in order to better understand the effects of injection timings on in-cylinder mixing and CAI combustion. The full engine cycle simulation including complete gas exchange and combustion processes was carried out over several cycles in order to obtain the stable cycle for analysis. The combustion models used in the present study are the Shell auto-ignition model and the characteristic-time combustion model, which were modified to take the high level of EGR into consideration. A liquid sheet breakup spray model was used for the droplet breakup processes.

Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to improve gasoline engines’ efficiency and simultaneously achieve ultra-low NOx emissions. Two of the primary obstacles for applying CAI combustion are the control of combustion phasing and the maximum heat release rate. To solve these problems, dimethyl ether (DME) was directly injected into the cylinder to generate multi-point micro-flame through compression in order to manage the entire heat release of gasoline in the cylinder through port fuel injection, which is known as micro-flame ignited (MFI) hybrid combustion.

Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), can improve the fuel economy of gasoline engines and simultaneously achieve ultra-low NOx emissions. However, the difficulty in combustion phasing control and violent combustion at high loads limit the commercial application of CAI combustion. To overcome these problems, stratified mixture, which is rich around the central spark plug and lean around the cylinder wall, is formed through port fuel injection and direct injection of gasoline. In this condition, rich mixture is consumed by flame propagation after spark ignition, while the unburned lean mixture auto-ignites due to the increased in-cylinder temperature during flame propagation, i.e., stratified flame ignited (SFI) hybrid combustion.

Gasoline Partially Premixed Combustion (PPC) is an advanced combustion concept to simultaneously reduce the NOx and soot emissions whilst retaining high engine efficiencies. In order to have a better understanding of gasoline PPC operation in terms of mixture formation, combustion and emissions characteristics, the investigation was carried out at 1200 bar injection pressure using the combination of thermodynamic and optical diagnostic analysis in a single cylinder common rail fuel injection engine with optical access. The PPC operation was achieved with a combination of high dilution and higher intake charge temperature at part-load condition using primary reference fuel (PRF). Split injections of two fuel distribution strategies (50:50 and 70:30) were studied.

Internal combustion engines are subjected to part-load operation more than in full load during a typical vehicle driving cycle. The problem with the Spark Ignition (SI) engine is its inherent low part-load efficiency. This problem arises due to the pumping loses that occur when the throttle closes or partially opens. One way of decreasing the pumping losses is to operate the engine lean or by adding residual gases. It is not possible to operate the engine unthrottled at very low loads due to misfire. However, the load can also be controlled by changing the intake valve closing timing - either early or late intake valve closing. Both strategies reduce the pumping loses and hence increase the efficiency. However the early intake valve closure (EIVC) can be used as mode transition from SI to CAI combustion.

Concerns over the impact of road transport emissions on the climate have led to increased focus on how CO2 emissions could be reduced from the sector. This is of particular concern in the commercial vehicle sector, where engine downsizing and electrification have limited benefit due to the vehicle duty cycle. In this paper, we present results from an experimental program to investigate the impact of dual fueling a heavy duty engine on hydrogen and diesel. Hydrogen is potentially a zero carbon fuel, if manufactured from renewable energy but could also be manufactured on the vehicle through steam reformation of part of the liquid fuel. This opens a novel pathway for the recovery of waste heat from the exhaust system through the endothermic steam reformation process, improving the overall system efficiency. For these concepts to be viable, it is essential the dual fueled combustion system is both thermally efficient, and does not increase toxic emissions such as NOx.

An experimental study has been carried out with the end goal of minimizing engine-out methane emissions with Premixed Micro Pilot Combustion (PMPC) in a natural gas-diesel Dual-Fuel™ engine. The test engine used is a heavy-duty single cylinder engine with high pressure common rail diesel injection as well as port fuel injection of natural gas. Multiple variables were examined, including injection timings, exhaust gas recirculation (EGR) percentages, and rail pressure for diesel, conventional Dual-Fuel, and PMPC Dual-Fuel combustion modes. The responses investigated were pressure rise rate, engine-out emissions, heat release and indicated specific fuel consumption. PMPC reduces methane slip when compared to conventional Dual-Fuel and improves emissions and fuel efficiency at the expense of higher cylinder pressure.