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Engine downsizing of the spark ignition gasoline engine is recognized as one of the most effective approaches to improve the fuel economy of a passenger car. However, further engine downsizing beyond 50% in a 4-stroke gasoline engine is limited by the occurrence of abnormal combustion events as well as much greater thermal and mechanical loads. In order to achieve aggressive engine downsizing, a boosted uniflow scavenged direct injection gasoline (BUSDIG) engine concept has been proposed and researched by means of CFD simulation and demonstration in a single cylinder engine. In this paper, the intake port design on the in-cylinder flow field and gas exchange characteristics of the uniflow 2-stroke cycle was investigated by computational fluid dynamics (CFD). In particular, the port orientation on the in-cylinder swirl, the trapping efficiency, charging efficiency and scavenging efficiency was analyzed in details.

Homogeneous charge compression ignition (HCCI) technology is promising to reduce engine exhaust emissions and fuel consumption. However, it is still confronted with the problem of its narrow operation range that covers only the light and medium loads. Therefore, to expand the operation range of HCCI, mode switching between HCCI combustion and transition SI combustion is necessary, which may bring additional problems to be resolved, including load fluctuation and increasing the complexity of control strategy, etc. In this paper, a continuously adjustable load strategy is proposed for gasoline engines. With the application of the strategy, engine load can be adjusted continuously by the in-cylinder residual gas fraction in the whole operation range. In this research, hybrid combustion is employed to bridge the gaps between HCCI and traditional SI and thus realize smooth transition between different load points.

In a previous paper [ 1 ], the authors have proposed a cost effective air hybrid concept based on a proprietary intake system and cam profile switching (CPS) system [ 2 ]. It was shown through engine simulations that the pneumatic hybrid operation could be achieved with about 15% regenerative efficiency. The proposed air hybrid operation can be achieved with proven technologies and engine components and hence it represents a cost-effective, reliable and quick deployable solution for low carbon vehicles. In this work, a four-cylinder 2 litre diesel engine has been modelled to operate on refined air hybrid engine configurations and the braking and motoring performance of each configuration have been studied. Both air hybrid systems can be constructed with production technologies and incur minimum changes to the existing engine design.

Over the last decade, the diesel engine has made dramatic progress in its performance and market penetration. However, in order to meet future emissions legislations, Nitrogen Oxides (NOx) and particulate matters' (PM) emissions will need to be reduced simultaneously. Nowadays researchers are focused on different combustion modes which can have a great potential for both low soot and low NOx. In order to achieve this, different injection strategies have been investigated. This study investigates the effects of split injection strategies with high levels of Exhaust Gas Recirculation (EGR) on combustion performance and emissions in a single-cylinder direct injection optical diesel engine. The investigation is focused on the effects of injection timing of split injection strategies. A Ricardo Hydra single-cylinder optical engine was used in which conventional experimental methods like cylinder pressure data, heat release analysis and exhaust emissions analysis were applied.

Controlled Auto-Ignition (CAI) combustion was realised in a production type 4-stroke 4-cylinder gasoline engine without intake charge heating or increasing compression ratio. The CAI engine operation was achieved using substantially standard components modified only in camshafts to restrict the gas exchange process The engine could be operated with CAI combustion within a range of load (0.5 to 4 bar BMEP) and speed (1000 to 3500 rpm). Significant reductions in both specific fuel consumption and CO emissions were found. The reduction in NOx emission was more than 93% across the whole CAI range. Though unburned hydrocarbons were higher under the CAI engine operation. In order to evaluate the potential of the CAI combustion technology, the European NEDC driving cycle vehicle simulation was carried out for two identical vehicles powered by a SI engine and a CAI/SI hybrid engine, respectively.

Water vapour is a main constituent of exhaust gas recirculation (EGR) in diesel engines and its influence on combustion and emissions were investigated. The following effects of the water vapour were examined experimentally: the effect of replacing part of the inlet charge oxygen (dilution effect), the effect of the higher specific heat capacity of water vapour in comparison with that of oxygen it replaces (thermal effect), the effect of dissociation of water vapour (chemical effect), as well as the overall effect of water vapour on combustion and emissions. Water vapour was introduced into the inlet charge, progressively, so that up to 3 percent of the inlet charge mass was displaced. This was equivalent to the amount of water vapour contained in 52 percent by mass of EGR for the engine operating condition tested in this work.

This is a first of a series of papers describing how the replacement of some of the inlet air with EGR modifies the diesel combustion process and thereby affects the exhaust emissions. This paper deals with only the reduction of oxygen in the inlet charge to the engine (dilution effect). The oxygen in the inlet charge to a direct injection diesel engine was progressively replaced by inert gases, whilst the engine speed, fuelling rate, injection timing, total mass and the specific heat capacity of the inlet charge were kept constant. The use of inert gases for oxygen replacement, rather than carbon dioxide (CO2) or water vapour normally found in EGR, ensured that the effects on combustion of dissociation of these species were excluded. In addition, the effects of oxygen replacement on ignition delay were isolated and quantified.

This is the second of a series of papers on how exhaust gas recirculation (EGR) affects diesel engine combustion and emissions. It concentrates on the effects of carbon dioxide (CO2) which is a principal constituent of EGR. Results are presented from a number of tests during which the nitrogen or oxygen in the engine inlet air was progressively replaced by CO2 and/or inert gases, whilst the engine speed, fuelling rate, injection timing, inlet charge total mass rate and inlet charge temperature were kept constant. In one set of tests, some of the nitrogen in the inlet air was progressively replaced by a carefully controlled mixture of CO2 and argon. This ensured that the added gas mixture had equal specific heat capacity to that of the nitrogen being replaced. Thus, the effects of dissociated CO2 on combustion and emissions could be isolated and quantified (chemical effect).

The extraction of small quantities of gas and particulates from diesel engine cylinders allows time-resolved gas and particulate analysis to be performed outside the engine during a short window of a few degrees crank angle at any stage of the engine cycle. The paper describes the design features and operation of a high-speed, intermittent sampling valve for extracting in-cylinder gases and particulates from diesel engines at any selected instant of the combustion process. Various sampling valve configurations are outlined. Detailed analysis of gas flow through the valve and the performance of the electromagnetic actuator and plunger are given in order to facilitate the design of the sampling valve. Finally, examples of the uses of the sampling valve in a direct-injection diesel engine are provided. These demonstrate how gaseous emissions such as NOx, uHC, CO2, and particulate emissions can be sampled at any part of the combustion process and analysed.

The measurement of the instantaneous flame temperature and soot concentration in the combustion chamber of a running diesel engine can provide useful information relating to the formation of two important exhaust pollutants, NOx and particulates. The two-colour method is based on optical pyrometry and it can provide estimates of the instantaneous flame temperature and soot concentration. The theoretical basis of the method is outlined in a companion paper. This paper deals with the practical problems involved in the construction of a working system, including suitable calibration techniques. The accuracy of the measurements of flame temperature and soot concentration is also discussed using results from a various sources.

The two-colour method is based on optical pyrometry and can readily be implemented at a modest cost for the measurement of the instantaneous flame temperature and soot concentration in the cylinders of diesel engines. With appropriate modification, this method can be applied to other continuous and intermittent combustion systems, such as those for gas turbine and boiler burners. This paper outlines the theoretical basis of the method, with particular attention being paid to the assumptions relating to the evaluation of the flame temperature and soot concentration. A companion paper deals with the practical problems involved in constructing a working system, including suitable calibration techniques, and assessment of the method accuracy.