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Controlled Auto Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), is one of the most promising combustion technologies to reduce the fuel consumption and NOx emissions. Currently, CAI combustion is constrained at part load operation conditions because of misfire at low load and knocking combustion at high load, and the lack of effective means to control the combustion process. Extending its operating range including high load boundary towards full load and low load boundary towards idle in order to allow the CAI engine to meet the demand of whole vehicle driving cycles, has become one of the key issues facing the industrialisation of CAI/HCCI technology. Furthermore, this combustion mode should be compatible with different fuels, and can switch back to conventional spark ignition operation when necessary. In this paper, the CAI operation is demonstrated on a 2-stroke gasoline direct injection (GDI) engine equipped with a poppet valve train.

Controlled Auto-Ignition (CAI) also known as Homogeneous Charge Compression Ignition (HCCI) is increasingly seen as a very effective way of lowering both fuel consumption and emissions. Hence, it is regarded as one of the best ways to meet stringent future emissions legislation. It has however, still many problems to overcome, such as limited operating range. This combustion concept was achieved in a production type, 4-cylinder gasoline engine, in two separated tests: naturally aspirated and turbocharged. Very few modifications to the original engine were needed. These consisted basically of a new set of camshafts for the naturally aspirated test and new camshafts plus turbocharger for the test with forced induction. After previous experiments with naturally aspirated CAI operation, it was decided to investigate the capability of turbocharging for extended CAI load and speed range.

One-dimensional engine simulation programmes are often used in the engine design and optimization studies. One of the key requirements of such a simulation programme is its ability to predict the heat release process during combustion. Such simulation software has built in it the heat release models for spark ignited premixed flame and compression ignited diesel combustion. The recent emergence of Controlled Auto Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI), has generated the need for a third type of heat release models for this new combustion process. In this paper, a heat release correlation for CAI combustion has been derived from extensive in-cylinder pressure data obtained from a Ricardo E6 single cylinder research engine and a multi-cylinder Port Fuel Injection (PFI) gasoline engine running with CAI combustion. The experimental data covered a wide range of air/fuel ratios, speed and percentage of residual gas.

Pumping Mean Effective Pressure (PMEP) is the main factor limiting the improvement of thermal efficiency in a spark-ignition (SI) engine under low load. One of the ways to reduce the pumping loss under low load is to use Cylinder DeActivation (CDA). The CDA aims at reducing the firing density (FD) of the SI engine under low load operation and increasing the mass of air-fuel mixture within one cycle in one cylinder to reduce the throttling effect and further reducing the PMEP. The multi-stroke cycles can also reduce the firing density of the SI engine after some certain reasonable design, which is feasible to improve the thermal efficiency of the engine under low load in theory. The research was carried out on a calibrated four-cylinder SI engine simulation platform. The thermal efficiency improvements of the 6-stroke cycle and 8-stroke cycle to the engine performance were studied compared with the traditional 4-stroke cycle under low load conditions.

A single cylinder, naturally aspirated, four-stroke and camless (Otto) engine was operated in homogeneous charge compression ignition (HCCI) mode with commercial gasoline. The valve timing could be adjusted during engine operation, which made it possible to optimize the HCCI engine operation for different speed and load points in the part-load regime of a 5-cylinder 2.4 liter engine. Several tests were made with differing combinations of speed and load conditions, while varying the valve timing and the inlet manifold air pressure. Starting with conventional SI combustion, the negative valve overlap was increased until HCCI combustion was obtained. Then the influences of the equivalence ratio and the exhaust valve opening were investigated. With the engine operating on HCCI combustion, unthrottled and without preheating, the exhaust valve opening, the exhaust valve closing and the intake valve closing were optimized next.

This paper describes the Lean Boost System, a gasoline engine concept for improved fuel economy. The system combines direct injection, lean operation and pressure charging, and allows significant reduction in swept volume, or ‘downsizing’. Engine tests have been undertaken which demonstrate the validity of the combustion concept. The strategy a typical manufacturer might adopt in order to meet future European requirements for CO2 emissions is proposed. Vehicle simulation results for typical North American and European vehicles are presented. Using the exhaust gas emission levels from engine tests and drive cycle simulation, aftertreatment requirements and configurations are considered.

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.

Future requirements for emission reduction from combustion engines in ground vehicles might be met by using the HCCI combustion concept. In this study, negative valve overlap (NVO) and low lift, short duration, camshaft profiles, were used to initiate HCCI combustion by increasing the internal exhaust gas recirculation (EGR) and thus retaining sufficient thermal energy for chemical reactions to occur when a pilot injection was introduced prior to TDC, during the NVO. One of the crucial parameters to control in HCCI combustion is the combustion phasing and one way of doing this is to vary the relative ratio of fuel injected in pilot and main injections. The combustion phasing is also influenced by the total amount of fuel supplied to the engine, the combustion phasing is thus affected when the load is changed. This study focuses on the reactions that occur in the highly diluted environment during the NVO when load and pilot to main ratio are changed.

An appropriate energy management strategy can further reduce the fuel consumption of P2 hybrid electric vehicles (HEV) with simple hybrid configuration and low cost. The rule-based real-time energy management strategy dominates the energy management strategies utilized in commercial HEVs, due to its robustness and low computational loads. However, its performance is sensitive to the setting of parameters and control actions. To further improve the fuel economy of a P2 HEV, the energy management strategy of the HEV has been re-designed based on the globally optimal control theory. An optimization strategy model based on the longitudinal dynamics of the vehicle and Bellman’s dynamic programming algorithm was established in this research and an optimal power split in the dual power sources including an internal combustion engine (ICE) and an electric machine at a given driving cycle was used as a benchmark for the development of the rule-based energy management strategy.

The work was concerned with experimental study of the turbulent flame development process of ethanol fuels in an optically accessed spark ignition research engine. The fuels were evaluated in a single cylinder engine equipped with full-bore overhead optical access and operated at typical stoichiometric part-load conditions. High-speed natural light (or chemiluminescence) imaging and simultaneous in-cylinder pressure data measurement and analysis were used to understand the fundamental influence of both low and high ethanol content on turbulent flame propagation and subsequent mass burning. Causes for the difference in cyclic variations were evaluated in detail, with comparisons made to existing burning velocity correlations where available.

Projected stringent emissions legislation will make tough demands on engine development. For diesel engines, in which combustion and emissions formation are governed by the spray formation and mixing processes, fuel injection plays a major role in the future development of cleaner engines. It is therefore important to study the fundamental features of the fuel injection process. In an engine the fuel is injected at high pressure into a pressurized and hot environment of air, which causes droplet formation and fuel evaporation. The injected fuel then forms a gaseous phase surrounding the liquid phase. The amount of evaporated fuel in relation to the total amount of injected fuel is of importance for engine performance, i.e. ignition delay and mixing rate. In this paper, the fraction of evaporated fuel was determined for sprays, using different orifice diameters ranging from 0.100 mm up to 0.227 mm, with the aid of a high-pressure spray chamber.

Future pressures to reduce the fuel consumption of passenger cars may require the exploitation of alternative combustion strategies for gasoline engines to replace, or use in combination with the conventional stoichiometric spark ignition (SSI) strategy. Possible options include homogeneous lean charge spark ignition (HLCSI), stratified charge spark ignition (SCSI) and homogeneous charge compression ignition (HCCI), all of which are intended to reduce pumping and thermal losses. In the work presented here four different combustion strategies were evaluated using the same engine: SSI, HLCSI, SCSI and HCCI. HLCSI was achieved by early injection and operating the engine lean, close to its stability limits. SCSI was achieved using the spray-guided technique with a centrally placed multi-hole injector and spark-plug. HCCI was achieved using a negative valve overlap to trap hot residuals and thus generate auto-ignition temperatures at the end of the compression stroke.

Experiments were performed using a Light-Duty, single-cylinder, research engine in which the emissions, fuel consumption and combustion characteristics of two Fischer-Tropsch (F-T) Diesel fuels derived from natural gas and two conventional Diesel fuels (Swedish low sulfur Diesel and European EN 590 Diesel) were compared. Due to their low aromatic contents combustion with the F-T Diesel fuels resulted in lower soot emissions than combustion with the conventional Diesel fuels. The hydrocarbon emissions were also significantly lower with F-T fuel combustion. Moreover the F-T fuels tended to yield lower CO emissions than the conventional Diesel fuels. The low emissions from the F-T Diesel fuels, and the potential for producing such fuels from biomass, are powerful reason for future interest and research in this field.

To achieve homogeneous charge compression ignition (HCCI) combustion in the range of low speeds and loads, special camshafts with low intake/exhaust cam lift and short intake/exhaust cam duration were designed. The camshafts were mounted in a Ricardo Hydra four-stroke single cylinder port fuel injection gasoline engine. HCCI combustion was achieved by controlling the amount of trapped residuals from previous cycle through negative valve overlap. The results show that indicated mean effective pressure (IMEP) depends on valve timings, engine speeds and lambda. Early exhaust valve closing (EVC) timings result in high residual fractions in the cylinder and low air mass sucked into the cylinder. As a result, combustion duration increases, IMEP and peak pressure decrease. However, pumping losses decrease. High engine speed has the similar effect on HCCI combustion characteristics as early EVC timings do. But inlet valve opening timings have slight effect on IMEP compared to EVC timings.

Global warming driven by “greenhouse gas” emissions is an increasingly serious concern of both the public and legislators. A potentially potent way to reduce these emissions and conserve fossil fuel resources is to use n-butanol, iso-butanol or octanol (2-ethylhexanol) from renewable sources as alternative fuels in diesel engines. The effects of adding these substances to diesel fuel were therefore tested in a single-cylinder heavy duty diesel engine operated using factory settings. These alcohols have better calorific values, flash points, lubricity, cetane numbers and solubility in diesel than shorter-chain alcohols. However, they have lower cetane numbers than diesel, so either hydrotreated vegetable oil (HVO) or Di-tertiary-butyl peroxide (DTBP) was added to the diesel-alcohol mixtures to generate blends with the same Cetane Number (CN) as diesel.

The need to reduce fuel consumption and CO2 emissions while meeting future emission legislation has lead to the investigation of alternative engines, transmissions, aftertreatment and control strategies. The evaluation of alternative configurations at the concept stage requires vehicle drive cycle simulation tools, which include the following features: Fast run-time Alternative transmission models Cold start effects on fuel consumption and emissions modeled After-treatment models. This paper describes the development of a MATLAB/SIMULINKTM - based drive cycle simulation model meeting these requirements. The paper includes validation data comparing fuel consumption, engine-out and tailpipe emissions for a direct injection gasoline vehicle with a stoichiometric/lean switching strategy and lean NOx catalyst.

In order to meet future emissions legislation for Diesel engines and reduce their CO2 emissions it is necessary to improve diesel combustion by reducing the emissions it generates, while maintaining high efficiency and low fuel consumption. Advanced injection strategies offer possible ways to improve the trade-offs between NOx, PM and fuel consumption. In particular, use of high EGR levels (⥸ 40%) together with multiple injection strategies provides possibilities to reduce both engine-out NOx and soot emissions. Comparisons of optical engine measurements with CFD simulations enable detailed analysis of such combustion concepts. Thus, CFD simulations are important aids to understanding combustion phenomena, but the models used need to be able to model cases with advanced injection strategies.

This study aims to improve the dual fuel combustion for low/zero carbon fuels. Seven cases were tested in a single cylinder optical engine and their ignition and combustion characteristics are compared. The baseline case is the conventional diesel combustion. Four cases are diesel-gas (compressed natural gas) dual-fuel combustion operations, and two cases are diesel-hythane combustion. The diesel fuel injection process was visualized by a high-speed copper vapour laser. The combustion processes were recorded with a high-speed camera at 10000 Hz with an engine speed of 1200 rpm. The high-speed recordings for each case included 22 engine cycles and were postprocessed to create one spatial overlapped average combustion image. The average combustion cycle images were then further thresholded and these images were then used in a new method to analyze the cycle-to-cycle variation in a dimensionless, for all cases comparable value.

Direct injection gasoline engines have the potential for improved fuel economy through principally the engine down-sizing, stratified charge combustion, and Controlled Auto Ignition (CAI). However, due to the limited time available for complete fuel evaporation and the mixing of fuel and air mixture, locally fuel rich mixture or even liquid fuel can be present during the combustion process of a direct injection gasoline engine. This can result in significant increase in UHC, CO and Particulate Matter (PM) emissions from direct injection gasoline engines which are of major concerns because of the environmental and health implications. In order to investigate and develop a more efficient DI gasoline engine, a camless single cylinder DI gasoline engine has been developed. Fully flexible electro-hydraulically controlled valve train was used to achieve spark ignition (SI) and Controlled Autoignition (CAI) combustion in both 4-stroke and 2-stroke cycles.