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A 2-stroke boosted uniflow scavenged direct injection gasoline (BUSDIG) engine was researched and developed at Brunel University London to achieve higher power-to-mass ratio and thermal efficiency. In the BUSDIG engine concept, the intake scavenge ports are integrated to the cylinder liner and controlled by the movement of piston top while exhaust valves are placed in the cylinder head. Systematic studies on scavenging ports, intake plenum, piston design, valve opening profiles and fuel injection strategies have been performed to investigate and optimise the scavenging performance and in-cylinder fuel/air mixing process for optimised combustion process. In order to achieve superior power performance with higher thermal efficiency, the evaluation and optimisation of the boost system for a 1.0 L 2-cylinder 2-stroke BUSDIG engine were performed in this study using one dimensional (1D) engine simulations.

A strategy to actualize the dual-mode (SI mode and HCCI mode) operation of gasoline engine was investigated. The 4VVAS (4 variable valve actuating system), capable of independently controlling the intake and exhaust valve lifts and timings, was incorporated into a specially designed cylinder head for a single cylinder research engine and a 4VVAS-HCCI gasoline engine test bench was established. The experimental research was carried out to study the dynamic control strategies for transitions between HCCI and SI modes on the HCCI operating boundaries. Results show that equipped with the 4VVAS cylinder head, the engine can be operated in HCCI or SI mode to meet the demands of different operating conditions. 4VVAS enables the rapid and effective control over the in-cylinder residual gas, and therefore dynamic transitions between HCCI and SI can be stably achieved. It is easier to achieve transition from HCCI to SI than reversely due to the influence of thermo-inertia.

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.

In this research, numerical simulation using Star-CD is performed to investigate the mixing process of a single-cylinder experimental gasoline engine equipped with 4VVAS (4 Variable Valve System). Different engine operating conditions are studied with respect to valve parameters, including EVC (Exhaust Valve Closing), IVO (Intake Valve Opening), and IVL (Intake Valve Lift). The definitions of RGF (Residual Gas Fraction)/temperature statistical distribution and inhomogeneity are proposed and quantified, on which the influences of the aforementioned valve parameters are analyzed. Results reveal that, the distribution of in-cylinder residuals varies with valve parameter combinations. Intake valve timing has a greater effect on the in-cylinder distribution and inhomogeneity of residuals than intake valve lift. Earlier IVO leads to lower RGF inhomogeneity around TDC.

Homogeneous Charge Compression Ignition (HCCI) has the potential of reducing fuel consumption as well as NOx emissions. However, it is still confronted with problems in real-time control system and control strategy for the application of HCCI, which are studied in detail in this paper. A CAN-bus-based distributed HCCI control system was designed to implement a layered close loop control for HCCI gasoline engine equipped with 4VVAS. Meanwhile, a layered management strategy was developed to achieve high real-time control as well as to simplify the couplings between the inputs and the outputs. The entire control system was stratified into three layers, which are responsible for load (IMEP) management; combustion phase (CA50) control and mechanical system control respectively, each with its own specified close loop control strategy. The system is outstanding for its explicit configuration, easy actualization and robust performance.

Controlled Auto-Ignition (CAI), also known as HCCI (Homogeneous Charge Compression Ignition), is increasingly seen as a very effective way of lowering both fuel consumption and emissions from gasoline engines. Therefore, it's seen as one of the best ways to meet future engine emissions and CO2 legislations. This combustion concept was achieved in a Ford production, port-injected, 4 cylinder gasoline engine. The only major modification to the original engine was the replacement of the original camshafts by a new set of custom made ones. The CAI operation was accomplished by means of using residual gas trapping made possible by the use of VCT (variable cam timing) on both intake and exhaust camshafts. When running on CAI, the engine was able to achieve CAI combustion with in a load range of 0.5 to 4.5 BMEP, and a speed range of 1000 to 3500 rpm. In addition, spark assisted CAI operation was employed to extend the operational range of low NOx and low pumping loss at part-load conditions.

The negative valve overlap has been shown as one of the most effective means to achieve controlled autoignition combustion in a four-stroke gasoline engine. A number of researches have been carried out on the performance and emission characteristics of CAI engines but there are still some fundamental questions that are yet to be addressed such as in-cylinder process. In the present study, a Ricardo Hydra single cylinder, four stroke optical gasoline engine was instrumented to investigate CAI combustion through negative valve overlap configuration. The effects of direct fuel injection timings and direct air injection at lambda 1 were studied by means of simultaneous in-cylinder heat release study and high speed images of complete chemiluminescence emission, OH and CHO radicals. In particular, the minor combustion process during the NVO period with various air injection quantities was studied with both heat release analysis and chemiluminescence results.

Controlled Auto-Ignition (CAI) combustion was investigated in a Ricardo E6 single cylinder, four-stroke gasoline engine. CAI combustion was achieved by employing positive valve overlap in combination with variable compression ratios and intake air temperatures. The combustion characteristics and emissions were studied in order to understand the major advantages and drawbacks of CAI combustion with positive valve overlap. The enlargement of the CAI operational region was obtained by boosting intake air and adding external EGR. The lean-boosted operation elevated the range of CAI combustion to the higher load region, whilst the use of external EGR allowed the engine to operate with CAI combustion in the region between boosted and N/A CAI operational ranges. The results were analyzed to investigate combustion characteristics, performance and emissions of the boosted CAI operations.

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.

The purpose of the European « SPACE LIGHT » (Whole SPACE combustion for LIGHT duty diesel vehicles) 3-year project launched in 2001 is to research and develop an innovative Homogeneous internal mixture Charged Compression Ignition (HCCI) for passenger cars diesel engine where the combustion process can take place simultaneously in the whole SPACE of the combustion chamber while providing almost no NOx and particulates emissions. This paper presents the whole project with the main R&D tasks necessary to comply with the industrial and technical objectives of the project. The research approach adopted is briefly described. It is then followed by a detailed description of the most recent progress achieved during the tasks recently undertaken. The methodology adopted starts from the research study of the in-cylinder combustion specifications necessary to achieve HCCI combustion from experimental single cylinder engines testing in premixed charged conditions.

The paper reports an investigation into the HCCI/CAI combustion process in a single cylinder optical engine. The auto-ignition and combustion processes of primary reference fuels were studied using the two-dimensional PLIF technique as well as heat release analyses. The formaldehyde formed during the low-temperature reactions of HCCI/CAI combustion was visualized by a PLIF system. The formaldehyde was excited by a Nd:YAG laser pumped tunable dye laser at 355nm wavelength and detected by a gated ICCD camera. Both temporal and spatial distributions of formaldehyde were measured during the auto-ignition processes of different primary reference fuels. The results have shown that the formation of formaldehyde and its subsequent disappearance were closely related to the start of the low temperature and high temperature heat release processes, respectively. The formation of formaldehyde was more affected by the charge temperature than by the fuel concentration.

Controlled Auto-Ignition (CAI) combustion, also known as HCCI or PCCI, has recently emerged as a viable alternative combustion process to the conventional spark ignition (SI) or compression ignition (CI) process for internal combustion (IC) engines, owing to its potential for high efficiency and extremely low emissions. One of the most effective and practical means of achieving CAI combustion in an engine is to retain or recycle the burnt gases. In order to understand better the effects of recycled burnt gases on CAI combustion, detailed analytical and experimental studies have been carried out. The analytical studies were performed using an engine simulation model with detailed chemical kinetics. The five effects of the recycled burned gases studied include: (1.) Charge heating effect: higher intake charge temperature due to hot burned gases; (2.) Dilution effect: the reduction of oxygen due to the presence of the burned gases; (3.)

This paper presents results from an experimental programme researching the in-cylinder conditions necessary to obtain homogenous CAI (or HCCI) combustion in a 4-stroke engine. The fuels under investigation include three blends of Unleaded Gasoline, a 95 RON Primary Reference Fuel, Methanol, and Ethanol. This work concentrates on establishing the CAI operating range with regard to Air/Fuel ratio and Exhaust Gas Re-circulation and their effect on the ignition timing, combustion rate and variability, Indicated thermal efficiency, and engine-out emissions such as NOx. Detailed maps are presented, defining how each of the measured variables changes over the entire CAI region. Results indicate that the alcohols have significantly higher tolerance to dilution than the hydrocarbon fuels tested. Also, variations in Gasoline blend have little effect on any of the combustion parameters measured.

The effects of Air/Fuel (A/F) ratios and Exhaust Gas Re-Circulation (EGR) rates on Homogeneous Charge Compression Ignition (HCCI) combustion of n-heptane have been experimentally investigated. The experiments were carried out in a single-cylinder, 4-stroke and variable compression-ratio engine equipped with a port fuel injector. Investigations concentrate on the HCCI combustion of n-heptane at different A/F ratios, EGR rates and their effects on knock limit, engine load, combustion variability, and engine-out emissions such as NOx, CO, and unburned HC. Variations of auto-ignition timings and combustion durations in the two-stage combustion process are analyzed in detail. Results show that HCCI combustion with a diesel type fuel can be implemented at room temperature with a conventional diesel engine compression-ratio. However, its knock limit occurs at very high A/F ratios, although high EGR rates can be tolerated.

In-cylinder flow was optimised in a three-valve twin-spark-plug SI engine in order to obtain good two-zone fuel fraction stratification in the cylinder by means of tumble flow. First, the in-cylinder flow field of the original intake system was measured by Particle Image Velocimetry (PIV). The results showed that the original intake system did not produce large-scale in-cylinder flow and the velocity value was very low. Therefore, some modifications were applied to the intake system in order to generate the required tumble flow. The modified systems were then tested on a steady flow rig. The results showed that the method of shrouding the lower part of the intake valves could produce rather higher tumble flow with less loss of the flow coefficient than other methods. The optimised intake system was then consisted of two shroud plates on the intake valves with 120° angles and 10mm height. The in-cylinder flow of the optimised intake system was investigated by PIV measurements.

Engine downsizing can effectively improve the fuel economy of spark ignition (SI) gasoline engines, but extreme downsizing is limited by knocking combustion and low-speed pre-ignition at higher loads. A 2-stroke SI engine can produce higher upper load compared to its naturally aspirated 4-stroke counterpart with the same displacement due to the double firing frequency at the same engine speed. To determine the potential of a downsized two-cylinder 2-stroke poppet valve SI gasoline engine with 0.7 L displacement in place of a naturally aspirated 1.6 L gasoline (NA4SG) engine, one-dimensional models for the 2-stroke gasoline engine with a single turbocharger and a two-stage supercharger-turbocharger boosting system were set up and validated by experimental results.

The spark-assisted compression ignition (SACI) is widely used to expend the high load limit of homogeneous charge compression ignition (HCCI), as it can reduce the high heat release rate effectively while partially maintain the advantage of high thermal efficiency and low NOx emission. But as engine load increases, the SACI combustion traditionally using negative valve overlap strategy (NVO) faces the drawback of higher pumping loss and limited intake charge availability, which lead to a restricted load expansion and a finite improvement of fuel economy. In this paper, research is focused on the SACI combustion using positive valve overlap (PVO) strategy. The characteristics of SACI combustion employing PVO strategy with external exhaust gas recirculation (eEGR) are investigated. Two types of PVO strategies are analyzed and compared to explore their advantages and defects, and the rules of adjusting SACI combustion with positive valve overlap are concluded.

Homogeneous charge compression ignition (HCCI) technology is promising to reduce engine exhaust emissions and fuel consumption in gasoline engine. However, it is still confronted with the problem of its limited operation range. High load is limited by the tradeoff between the quantity of working charge and dilution charge. Low load is limited by the high residual gas fraction and low temperature in the cylinder. One of the highlights of HCCI combustion research at present is to expand the low load limit of HCCI combustion by developing HCCI idle operation. The main obstacle in developing HCCI idle combustion is too high residual gas fraction and low temperature to misfire in cylinder. This paper relates to a method for achieving the appropriate environment for auto-ignition at idle and the optimal tradeoff between the combustion stability and fuel consumption by employing EIVO valve strategy with an equivalent air-fuel ratio.

In order to extend the CAI operation range in 4-stroke mode and maximize the benefit of low fuel consumption and emissions in CAI mode, 2-stroke CAI combustion is revived operating in a GDI engine with poppet valves, where the conventional crankcase scavenging is replaced by boosted scavenging. The CAI combustion is achieved through the inherence of the 2-Stroke operation, which is retaining residual gas. A set of flexible hydraulic valve train was installed on the engine to vary the residual gas fraction under the boosting condition. The effects of spark timing, intake pressure and short-circuiting on 2-stroke CAI combustion and its emissions are investigated and discussed in this paper. Results show the engine could be controlled to achieve CAI operation over a wide range of engine speed and load in the 2-stroke mode because of the flexibility of the electro-hydraulic valvetrain system.

Chemical reaction kinetics plays an important role in homogeneous charge compression ignition (HCCI) combustion. In order to control the combustion process, the underlying mechanism of auto-ignition must be explored, especially for the HCCI combustion using negative valve overlap (NVO) strategy, in which the residual gas affects the auto-ignition of next cycle remarkably. In this research, experimental research was carried out in a single cylinder gasoline engine equipped with an in-cylinder sampling system which mainly consists of a special spark plug, a sampling tube and a high-speed electromagnetic valve. In-cylinder charge was sampled at compression stroke and analyzed by FTIR with two types of fuel injection strategy, such as port fuel injection (PFI) solely and port fuel injection combined with injection during negative valve overlap (PFI & NVO-Injection).