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In the automotive industry, engine downsizing has been widely accepted as an enabler to improving the fuel economy and reducing the CO₂ emissions. The Atkinson cycle is one of the key technologies. In this paper, the Atkinson cycle with different expansion ratios are compared and analyzed. The investigation is compared with the benchmark whose expansion and compression ratio are identical. The aim is to understand the inherent characteristics of the over-expansion and its effect on the engine performance and emissions. The simulation results show that, the Atkinson cycle produces higher efficiency due to over-expansion. The Atkinson cycle has higher internal EGR compared with the benchmark at equivalent conditions, which contributes to lower the NOx and CO emissions.

It is well known that direct injection (DI) is a technology enabler for stratified combustion in spark-ignition (SI) engines. At full load or wide-open throttle (WOT), partial charge stratification can suppress knock, enabling greater spark advance and increased torque. Such split-injection or double-pulse injection strategies are employed when using gasoline in DI (GDI). However, as the use of biofuels is set to increase, is this mode still beneficial? In the current study, the authors attempt to answer this question using two gasoline-alternative biofuels: firstly, ethanol; the widely used gasoline-alternative biofuel and secondly, 2,5-dimethylfuran (DMF); the new biofuel candidate. These results have been benchmarked against gasoline in a single-cylinder, spray-guided DISI research engine at WOT (λ = 1 and 1500 rpm). Firstly, single-pulse start of injection (SOI) timing sweeps were conducted with each fuel to find the highest volumetric efficiency and IMEP.

Conventional diesel-fuelled Partially Premixed Compression Ignition (PPCI) engines have been investigated by many researchers previously. However, the ease of ignition and difficulty of vaporization of diesel fuel make it imperfect for PPCI combustion. In this study, dieseline (blending of diesel and gasoline) was looked into as the Partially Premixed Compression Ignition fuel for its combination of two fuel properties, ignition-delay-increasing characteristics and higher volatility, which make it more suitable for PPCI combustion compared to neat diesel. A series of tests were carried out on a Euro IV light-duty common-rail diesel engine, and different engine modes, from low speed/load to middle speed/load were all tested, under which fuel blend ratios, EGR rates, injection timings and quantities were varied. The emissions, fuel consumption and combustion stability of this dieseline-fuelled PPCI combustion were all investigated.

Pilot injection has been used widely in diesel engines for its NOx and noise reducing characteristics. In this paper, its impacts to the particle emissions were studied using a light-duty common-rail Euro 4 diesel engine with different pilot injection strategies. Three steady-state engine modes were selected from the EU legislative diesel engine test cycle to represent low, medium and high engine speeds and loads. The quantities and injection timings of the pilot injection strategies were then varied. The particle number concentration and size distributions were investigated along with the smoke and regulated gas emissions such as the NOx trade-off. These results indicate how a pilot injection alongside a main injection can increase the particle size compared to a single main injection event. Furthermore, the split injection was closely related to the engine mode.

In this study, the particle emission characteristics of 10% alternative diesel fuel blends (Rapeseed Methyl Ester and Gas-to-Liquid) were investigated through the tests carried out on a light duty common-rail Euro 4 diesel engine. Under steady engine conditions, the study focused on particle number concentration and size distribution, to comply with the particle metrics of the European Emission Regulations (Regulation NO 715/2007, amended by 692/2008 and 595/2009). The non-volatile particle characteristics during the engine warming up were also investigated. They indicated that without any modification to the engine, adding selected alternative fuels, even at a low percentage, can result in a noticeable reduction of the total particle numbers; however, the number of nucleation mode particles can increase in certain cases.

The paper presents analysis of performance and emission characteristics of a common rail diesel engine operating with RME, with and without EGR. In both cases, the RME fuel was pre-heated in a heat exchanger to control its temperature before being pumped to the common rail. The studied parameters include the in-cylinder pressure history, rate of heat release, mass fraction burned, and exhaust emissions. The results show that when the fuel temperature increases and the engine is operated without EGR, the brake specific fuel consumption (bsfc) decreases, engine efficiency increases and NOx emission slightly decreases. However, when EGR is used while fuel temperature is increased, the bsfc and engine efficiency is independent of fuel temperature while NOx slightly increases.

The differences between modern diesel and gasoline engine configurations are now becoming smaller and smaller, and in fact will be even smaller in the near future. They will all use moderately high compression ratios and complex direct injection strategies. The HCCI combustion mode is likely to lead to the merging of gasoline and diesel engine technologies to handle the challenges they are facing, offering a number of opportunities for the development of the fuels, engine control and after-treatment. The authors' recent experimental research into the HCCI combustion quality of gasoline and diesel blend fuels has referred to the new combustion technology as ‘Dieseline’.

The effects of variable intake-valve-timing on the gas exchange process and performance of a 4-valve direct-injection HCCI engine were computationally investigated using a 1D gas dynamics engine cycle simulation code. A non-typical strategy to actuate the pair of intake valves was examined; whereby each valve was assumed to be actuated independently at different timing. Using such an intake valves strategy, the obtained results showed a considerable improvement of the engine parameters such as load and charging efficiency as compared with the typical identical intake valve pair timings case. Additional benefits of minimizing pumping losses and improving the fuel economy were demonstrated with the use of the non-simultaneous actuation of the intake valve pair having the opening timing of the early intake valve coupled with a symmetric degree of crank angle for the timing of exhaust valve closing.

Homogeneous Charge Compression Ignition (HCCI) has emerged as a promising technology for reduction of exhaust emissions and improvement of fuel economy of internal combustion engines. There are generally two proposed methods of realizing the HCCI operation. The first is through the control of gas temperature in the cylinder and the second is through the control of chemical reactivity of the fuel and air mixture. EGR trapping, i.e., recycling a large quantity of hot burned gases by using special valve-train events (e.g. negative valve overlap), seems to be practical for many engine configurations and can be combined with any of the other HCCI enabling technologies. While this method has been widely researched, it is understood that the operating window of the HCCI engine with negative valve overlap is constrained, and the upper and lower load boundaries are greatly affected by the in-cylinder temperature.

The objective of the current research was to predict and analyze the flow through the grill of air intake system which is positioned behind the front wheel arch of vehicle. Most of the vehicle used today locates the grill of air intake at the front side so to acquire benefit of ram effect. In some cases, however, the grill is located behind the vehicle to improve wading performance. The geometry of air intake system of Land Rover Freelander was used in the modelling approach. The study was focused on different flow speeds on the grill at high load operation where the air speed at the grill side is high and creates negative pressure. The CFD results are validated against experimental data of steady flow test bench.

This paper presents a computational investigation of the in-cylinder charge characteristics within a motored 4-valve direct injection HCCI engine cylinder with applied negative valve overlapping. Non-typical intake valve strategy was investigated; whereby the pair of intake valves was assumed to follow the same low-lift short-duration valve-lift profile but actuated at different timings. The phase of intake-valve-opening relative to that of exhaust-valve-closing was optimized in terms of pumping losses. The flow fields generated with such an intake valve strategy were compared to those produced in the same engine cylinder but with typical early and late intake-valve-timing. The computational results of such an approach showed modifications in the in-cylinder swirl and tumble motions during the intake and compression strokes.

This paper presents a computational study of the airflow features within a motored 4-valve direct injection engine cylinder. An unconventional intake valve strategy was investigated; whereby each valve on the pair of intake valves was assumed to be actuated with different lifts and duration. One of the intake valves was assumed to follow a high-lift long duration valve-lift profile while the other was assumed to follow a low-lift short duration valve-lift profile. The pair of exhaust valves was assumed to be actuated with two identical low-lift short duration valve-lift profiles in order to generate the so-called negative valve overlapping (NVO). The in-cylinder flow fields developed with such intake valve strategy were compared to those produced in the same engine cylinder but with the application of identical low-lift short duration intake valve events.

Particulate Emissions from Homogeneous Charge Compression Ignition (HCCI) combustion are routinely assumed to be negligible. It is shown here that this is not the case when HCCI combustion is implemented in a direct injection gasoline engine. The conditions needed to sustain HCCI operation were realized using the negative valve overlap method for trapping high levels of residual exhaust gases in the cylinder. Measurements of emitted particle number concentration and electrical mobility diameter were made with a Cambustion DMS500 over the HCCI operating range possible with this hardware. Emissions of oxides of nitrogen, carbon monoxide and unburned hydrocarbons were also measured. These data are presented and compared with similar measurements made under conventional spark ignition (SI) operation in the same engine. Under both SI and HCCI operation, a significant accumulation mode was detected with particle equivalent diameters between 80 and 100 nm.

This paper focuses on supercharged HCCI engines employing internal EGR that is obtained by the use of negative valve overlap. In HCCI engines, the absence of throttling coupled with the use of high compression ratio to facilitate auto-ignition and with the use of lean mixtures result in improved fuel efficiency. High dilution is required to control the auto-ignition and it also results in reduction of the production of NOx. To compensate for the charge dilution effect, the method used to recover the loss of power is to introduce more air in to the engine which allows introducing also more fuel while maintaining high lambda. A supercharger is required to introduce the required amount of air into the engine. The modelling investigation performed with Ricardo WAVE® coupled with CHEMKIN® and experimental investigation for supercharged HCCI show significant improvement in terms of extension of load range and reduction of NOx over the naturally aspirated HCCI and also over SI operation.

It is well-known that gasoline is a poor fuel for HCCI operation due to its high autoignation temperature, while the major problem for diesel HCCI is that the ignition temperature of diesel fuel is too low so that diesel autoignites too early. Interestingly a blend of gasoline and diesel fuel could have desirable characteristics for HCCI operation. The negative valve overlap (NVO) is a practical and feasible control mode for production applications of the HCCI concept. At present, the most serious problem is the difficulty to control the moment of auto-ignition and extend the limited operating window of smooth HCCI operation. In this paper, the promotive effects of diesel fuel on gasoline HCCI combustion were experimentally examined. The diesel fuel as additive was added in advance in different proportion (10% and 20% by mass) into gasoline for the purpose of improving its ignitability. The experiments conducted on a gasoline HCCI engine which was naturally aspirated and unthrottled.

There is a worldwide interest in the research of various alternative fuels for automotive engines for the purpose of reduction of CO2 and toxically harmful exhaust emissions. Coal-bed gas, the main component of which is methane, has been considered an attractive alternative fuel for combustion engines due to its abundant resources, high hydrogen-carbon ratios and very low soot formation tendency. The composition of available coal-bed gas, however, can vary considerably, and this has made its combustion stability difficult to control in conventional spark ignition engines. To overcome the problem, a combustion system with a swirl chamber connected to the main combustion chamber through an orifice has been developed for the use of coal-bed gas in spark ignition engines, and the corresponding combustion process has been studied using a developed combustion model involving flame kernel formation and flame front propagation.

Gasoline and diesel, the two fuels with very different characteristics and with wide availability for conventional engine use, were blended as a HCCI engine fuel. Gasoline, with high volatility, easy vaporization and mixture formation, is used to form the homogeneous charge. Diesel fuel which has good ignitability and fast combustion at the conditions predominating in the HCCI environment, is used to dominate the auto-ignition and restrain the knocking combustion. It is expected that these two different fuels with opposite but complementary properties can be used to reach a good compromise in HCCI combustion. Experiments, conducted with moderate compression ratios (CR) and using two modes of HCCI control, i.e. intake heating with CR 15.0 and negative valve overlap (NVO) with CR 10.4, yielded results that prove this expectation.

Liquefied alternative fuels offer great potential benefits in reducing exhaust emissions and improving fuel economy of automotive engines. In order to achieve the best performance of the engine running with such fuels, it is critical to have an appropriate fuel system. In the present work, a new electronically controlled common-rail injection system has been specially designed and tested for the direct injection of liquefied alternative fuels, since a conventional pump-line-injector injection system in the conventional diesel engine was not suitable for the purpose. Experimental work has been carried out to examine and improve matching of the fuel injection system on a new fuel injection pump test bench. The preliminary engine bench test has demonstrated that this arrangement meets the requirement for the operating characteristics of a fuel injection system in a direct injection diesel engine operating with dimethyl ether (DME).

With boosted HCCI operation on gasoline using residual gas trapping, the amount of residuals was found to be of importance in determining the boundaries of stable combustion at various boost pressures. This paper represents a development of this approach by concentrating on the effects of inlet valve events on the parameters of boosted HCCI combustion with residual gas trapping. It was found that an optimum inlet valve timing could be found in order to minimize NOx emissions. When the valve timing is significantly advanced or retarded away from this optimum, NOx emissions increase due to the richer air / fuel ratios required for stable combustion. These richer conditions are necessary as a result of either the trapped residual gases becoming cooled in early backflow or because of lowering of the effective compression ratio. The paper also examines the feasibility of using inlet valve timing as a method of controlling the combustion phasing for boosted HCCI with residual gas trapping.

This paper presents a modeling study of a gasoline HCCI engine using a single-zone and a multi-zone engine combustion models coupled with the CHEMKIN chemical kinetics solver for the closed part of the cycle. These combustion models are subsequently combined with a 1-D gas dynamics engine cycle simulation code which calculates the engine gas exchange to supply the boundary conditions for the in-cylinder simulation and also predicts engine performance. The simulated in-cylinder pressure history and charge composition at the time of exhaust valve opening are compared with the data from a parallel engine experimental project. Although the single-zone model is useful for parameter studies by predicting the trend of auto-ignition timing variations as the result of the effect of engine operating conditions, the matching of simulated and test data is good perhaps only if the mixture and temperature distributions in the cylinder are uniform.