Search Results

Pre-chamber combustion (PCC) has re-emerged in recent last years as a potential solution to help to decarbonize the transport sector with its improved engine efficiency as well as providing lower emissions. Research into the combustion process inside the pre-chamber is still a challenge due to the high pressure and temperatures, the geometrical restrictions, and the short combustion durations. Some fundamental studies in constant volume combustion chambers (CVCC) at low and medium working pressures have shown the complexity of the process and the influence of high pressures on the turbulence levels. In this study, the pre-chamber combustion process was investigated by combustion visualization in an optically-accessible pre-chamber under engine relevant conditions and linked with the jet emergence inside the main chamber. The pre-chamber geometry has a narrow-throat. The total nozzle area is distributed in two six-hole rows of nozzle holes.

Demand for transport energy is growing but this growth is skewed heavily toward commercial transport, such as, heavy road, aviation, marine and rail which uses heavier fuels like diesel and kerosene. This is likely to lead to an abundance and easy availability of lighter fractions like naphtha, which is the product of the initial distillation of crude oil. Naphtha will also require lower energy to produce and hence will have a lower CO₂ impact compared to diesel or gasoline. It would be desirable to develop engine combustion systems that could run on naphtha. Many recent studies have shown that running compression ignition engines on very low Cetane fuels, which are very similar to naphtha in their auto-ignition behavior, offers the prospect of developing very efficient, clean, simple and cheap engine combustion systems. Significant development work would be required before such systems could power practical vehicles.

The paper discusses the concept, design and final results from the ‘Ultra Boost for Economy’ collaborative project, which was part-funded by the Technology Strategy Board, the UK's innovation agency. The project comprised industry- and academia-wide expertise to demonstrate that it is possible to reduce engine capacity by 60% and still achieve the torque curve of a modern, large-capacity naturally-aspirated engine, while encompassing the attributes necessary to employ such a concept in premium vehicles. In addition to achieving the torque curve of the Jaguar Land Rover naturally-aspirated 5.0 litre V8 engine (which included generating 25 bar BMEP at 1000 rpm), the main project target was to show that such a downsized engine could, in itself, provide a major proportion of a route towards a 35% reduction in vehicle tailpipe CO2 on the New European Drive Cycle, together with some vehicle-based modifications and the assumption of stop-start technology being used instead of hybridization.

In the engine community, gasoline compression ignition (GCI) engines are at the forefront of research and efforts are being taken to commercialize an optimized GCI engine in the near future. GCI engines are operated typically at Partially Premixed Combustion (PPC) mode as it offers better control of combustion with improved combustion stability. While the transition in combustion homogeneity from convectional Compression Ignition (CI) to Homogenized Charge Compression Ignition (HCCI) combustion via PPC has been comprehensively investigated, the physical and chemical effects of fuel on GCI are rarely reported at different combustion modes. Therefore, in this study, the effect of physical and chemical properties of fuels on GCI is investigated. In-order to investigate the reported problem, low octane gasoline fuels with same RON = 70 but different physical properties and sensitivity (S) are chosen.

Engine thermal management systems (TMS) are gaining importance in engine development and calibration to achieve low fuel consumption and meet future emissions standards. To benefit from their full potential, a thorough understanding of the effects on engine behavior is necessary. Steady state tests were performed on a 2.0L direct injection diesel engine at different load points. A design of experiments (DoE) approach was used to conduct exhaust gas recirculation (EGR) and injection timing swings at different coolant temperatures. The effect of the standard engine controller and calibration was observed during these tests. The injection timing strategy included a significant dependency on coolant temperature, retarding injection by about 3° crank angle between coolant temperatures of 70°C and 86°C. In contrast, EGR strategy was essentially independent of coolant temperature, though physical interactions were present due in part to the EGR cooler.

As part of a larger programme of work on the integrated control of engine and transmissions a study has been made of the control aspects of the transmission with a detailed investigation of the hydraulic circuit. The requirements of the broader programme necessitated an electrical input for the transmission control and a test bed version was successfully modified with electro-hydraulic valves. Attention to detail in the design of the hydraulic circuit and the control of operating pressure can bring significant benefits to the transmission efficiency with consequent beneficial effects on fuel economy. This paper investigates several aspects of the components used and their effect on efficiency, in particular pump sizing. This investigation is illustrated with results from a computer simulation of the system. Possible improvements through a modified control strategy for the belt pressure are also proposed with steady state results obtained experimentally from the test bed transmission.

Increasing the number of cold-start engine cycles which could be run in any one day would greatly improve the productivity of an engine test facility. However with the introduction of forced cooling procedures there is the inherent risk that test-to-test repeatability will be affected. Therefore an investigation into the effects caused by forced cooling on fuel consumption and the temperature distribution through the engine and fluids is essential. Testing was completed on a 2.4 litre diesel engine running a cold NEDC. The test facility utilises a basic ventilation system, which draws in external ambient air, which is forced past the engine and then drawn out of the cell. This can be supplemented with the use of a spot cooling fan. The forced cool down resulted in a much quicker cool down which was further reduced with spot cooling, in the region of 25% reduction.

Wankel rotary engines are becoming an increasingly popular area of research with regard to their use as a range extender in the next generation of Hybrid Electric Vehicle (HEV). Due to their simple design, lightness, compactness and very favourable power-to-weight ratio, they represent one of the best alternative solutions to classic reciprocating piston engines. On the other hand, current Wankel engines still need improvements in terms of specific fuel consumption and emissions. This paper describes an innovative approach for the assessment of the performance of a modern rotary engine. All the experimental activities will be carried out within the Innovate UK funded ADAPT Intelligent Powertrain project led by Westfield Sportscars Limited.

The paper discusses investigations into improving the full-load and transient performance of the Ultraboost extreme downsizing engine by the application of the SuperGen variable-speed centrifugal supercharger. Since its output stage speed is decoupled from that of the crankshaft, SuperGen is potentially especially attractive in a compound pressure-charging system. Such systems typically comprise a turbocharger, which is used as the main charging device, compounded at lower charge mass flow rates by a supercharger used as a second boosting stage. Because of its variable drive ratio, SuperGen can be blended in and out continuously to provide seamless driveability, as opposed to the alternative of a clutched, single-drive-ratio positive-displacement device. In this respect its operation is very similar to that of an electrically-driven compressor, although it is voltage agnostic and can supply other hybrid functionality, too.

The European Particle Measurement Program (PMP) defines the current standard for measurement of Particle Number (PN) emissions from vehicles in Europe. This specifies a 50% count efficiency (D50) at 23 nm and a 90% count efficiency (D90) at 41 nm. Particulate emissions from Gasoline Direct Injection (GDI) engines have been widely studied, but usually only in the context of PMP or similar sampling procedures. There is increasing interest in the smallest particles - i.e. smaller than 23 nm - which can be emitted from vehicles. The literature suggest that by moving D50 to 10 nm, PN emissions from GDI engines might increase by between 35 and 50% but there remains a lot of uncertainty.

Knock in spark ignition engines is stochastic in nature. It is caused by autoignition in hot spots in the unburned end-gas ahead of the expanding flame front. Knock onset in an engine cycle can be predicted using the Livengood-Wu integral if the variation of ignition delay with pressure and temperature as well as the pressure and temperature variation with crank angle are known. However, knock intensity (KI) is determined by the evolution of the pressure wave following knock onset. In an earlier paper (SAE 2017-01-0689) we showed that KI can be approximated by KI = Z (∂T/∂x)-2 at a fixed operating condition, where Z is a function of Pko, the pressure, and (∂T/∂x) is the temperature gradient in the hot spot at knock onset. Then, from experimental measurements of KI and Pko, using five different fuels, with the engine operating at boosted conditions, a probability density function for (∂T/∂x) was established.

Pre-chamber combustion (PCC) is a promising engine combustion concept capable of extending the lean limit at part load. The engine experiments in the literature showed that the PCC could achieve higher engine thermal efficiency and much lower NOx emission than the spark-ignition engine. Improved understanding of the detailed flow and combustion physics of PCC is important for optimizing the PCC combustion. In this study, we investigated the gas exchange and flame jet from a narrow throat pre-chamber (PC) by only fueling the PC with methane in an optical engine. Simultaneous negative acetone planar laser-induced fluorescence (PLIF) imaging and OH* chemiluminescence imaging were applied to visualize the PC jet and flame jet from the PC, respectively. Results indicate a delay of the PC gas exchange relative to the built-up of the pressure difference (△ P) between PC and the main chamber (MC). This should be due to the gas inertia inside the PC and the resistance of the PC nozzle.

The Divided Exhaust Period (DEP) concept is an approach which has been proved to significantly reduce the averaged back pressure of turbocharged engines whilst still improving its combustion phasing. The standard layout of the DEP system comprises of two separately-functioned exhaust valves with one valve feeding the blow-down pulse to the turbine whilst the other valve targeting the scavenging behaviour by bypassing the turbine. Via combining the characteristics of both turbocharged engines and naturally aspirated engines, this method can provide large BSFC improvement. The DEP concept has only been applied to single-stage turbocharged engines so far. However, it in its basic form is in no way restricted to a single-stage system. This paper, for the first time, will apply DEP concept to a regulated two-stage (R2S) downsized SI engine.

Currently, 80% of European diesel passenger cars are turbocharged and as emission standards become more stringent exhaust gas recirculation (EGR) will be the primary means of suppressing oxides of nitrogen (NOx). The lighter the load the greater will be the combustion tolerance to increased EGR flow rates and hence increased NOx suppression. Automotive diesel engines using wastegated turbochargers cannot recirculate above 50% EGR without some sort of “added” device or system, which is able to displace the inlet fresh air charge. This has been demonstrated by throttling the diesel intake to reduce the fresh air inlet manifold pressure so allowing more EGR flow by virtue of a higher exhaust-side pressure due the effects of the turbocharger. The method reported here investigates a different approach to increasing the EGR rates by replacing a fixed geometry turbocharger (FGT) with a variable geometry turbocharger, (VGT).

Toluene primary reference fuel (TPRF) (mixture of toluene, iso-octane and heptane) is a suitable surrogate to represent a wide spectrum of real fuels with varying octane sensitivity. Investigating different surrogates in engine simulations is a prerequisite to identify the best matching mixture. However, running 3D engine simulations using detailed models is currently impossible and reduction of detailed models is essential. This work presents an AramcoMech reduced kinetic model developed at King Abdullah University of Science and Technology (KAUST) for simulating complex TPRF surrogate blends. A semi-decoupling approach was used together with species and reaction lumping to obtain a reduced kinetic model. The model was widely validated against experimental data including shock tube ignition delay times and premixed laminar flame speeds. Finally, the model was utilized to simulate the combustion of a low reactivity gasoline fuel under partially premixed combustion conditions.

A number of studies have been carried out examining the impact of biodiesel blend ratio on vehicle performance and emissions, however there is relatively little data available on the interaction between blend ratio and reduced ambient temperatures over the New European Drive Cycle (NEDC). This study examines the effects of increasing the blend ratio of Rapeseed Methyl Ester (RME) on the NEDC fuel consumption and tailpipe emissions of a vehicle equipped with a 2.0 litre common rail diesel engine, tested on a chassis dynamometer at ambient temperatures of 25, 10 & −5°C. This study found that under low temperature ambient conditions increasing blend ratios had a significant detrimental effect on vehicle particulate emissions reversing the benefits observed at higher ambient temperatures. Blend ratio was found to have minimal impact on hydrocarbon emissions regardless of ambient temperature while carbon monoxide and NOx emissions were found to increase by up to 20% and 5.5% respectively.

Primary Reference Fuels (PRFs) - binary mixtures of n-heptane and iso-octane based on Research Octane Number (RON) - are popular gasoline surrogates for modeling combustion in spark ignition engines. The use of these two component surrogates to represent real gasoline fuels for simulations of HCCI/PCCI engines needs further consideration, as the mode of combustion is very different in these engines (i.e. the combustion process is mainly controlled by the reactivity of the fuel). This study presents an experimental evaluation of PRF surrogates for four real gasoline fuels termed FACE (Fuels for Advanced Combustion Engines) A, C, I, and J in a motored CFR (Cooperative Fuels Research) engine. This approach enables the surrogate mixtures to be evaluated purely from a chemical kinetic perspective. The gasoline fuels considered in this study have very low sensitivities, S (RON-MON), and also exhibit two-stage ignition behavior.

This paper investigates the potential for reduced NOx emissions from the integration of thermal factors into the Diesel engine calibration process. NOx emissions from Diesel engines have been shown to be sensitive to engine operating temperature, which is directly related to the level of cooling applied to the engine, in addition to the main engine operating parameters such as injection timing and EGR ratio. Experimental engine characterization of the main engine parameters against coolant temperature set point shows that engine cooling settings can extend the feasible lower limits of fuel consumption and emissions output from Diesel engine. With the adoption of an integrated calibration methodology including engine cooling set point, NOx emissions can be improved by up to 30% at crucial high speed/load operating points seen in the NEDC drive cycle with a minor reduction in fuel economy and small increase in CO output.

This paper gives an overview of the development of a number of loss models for the pushing metal V-belt CVT. These were validated using a range of experimental data collected from two test rigs. There are several contributions to the torque losses and new models have been developed that are based upon relative motion between belt components and pulley deflections. Belt slip models will be proposed based upon published theory, expanded to take account of new findings from this work. The paper introduces a number of proposals to improve the efficiency of the transmission based on redesign of the belt geometry and other techniques to reduce frictional losses between components. These proposed efficiency improvements have been modelled and substituted into a complete vehicle simulation to show improvements in vehicle fuel economy over a standard European drive cycle.

If fuels that are more resistant to auto-ignition are injected near TDC in compression ignition engines, they ignite much later than diesel fuel and combustion occurs when the fuel and air have had more chance to mix. This helps to reduce NOX and smoke emissions at much lower injection pressures compared to a diesel fuel. However, PPCI (Partially Premixed Compression Ignition) operation also leads to higher CO and HC at low loads and higher heat release rates at high loads. These problems can be significantly alleviated by managing the mixing through injector design (e.g. nozzle size and centreline spray angle) and changing CR (Compression Ratio). This work describes results of running a single-cylinder diesel engine on fuel blends by using three different nozzle design (nozzle size: 0.13 mm and 0.17 mm, centreline spray angle: 153° and 120°) and two different CRs (15.9:1 and 18:1).