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SI-CAI hybrid combustion, also known as spark-assisted compression ignition (SACI), is a promising concept to extend the operating range of CAI (Controlled Auto-Ignition) and achieve the smooth transition between spark ignition (SI) and CAI in the gasoline engine. In order to investigate the effect of the thermal boundary condition on the hybrid combustion, the experiments with different coolant temperatures are performed to adjust the chamber wall temperature in a gasoline engine. The experimental results indicate that increasing wall temperature would advance the combustion phasing, enlarge the peak heat release rate and shorten the combustion duration. While the capacity of the wall temperature effect on the hybrid combustion characteristics are more notable in the auto-ignition dominated hybrid combustion.

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.)

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.

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.

This paper is a complementary to previous investigations by the authors (1,2,3,4) on the different effects of EGR on combustion and emissions in DI diesel engine. In addition to the several effects that cold EGR has on combustion and emissions the application of hot EGR results in increasing the inlet charge temperature, thereby, for naturally aspirated engines, lowering the inlet charge mass due to thermal throttling. An associated consequence of thermal throttling is the reduction in the amount of oxygen in the inlet charge. Uncooled EGR, therefore, affects combustion and emissions in two ways: through the reduction in the inlet charge mass and through the increase in inlet charge temperature. The effect on combustion and emissions of increasing the inlet charge temperature (without reducing the inlet charge mass) has been dealt with in ref. (1).

The present paper aims to investigate the influence of spark ignition on CAI combustion based on internal EGR strategy. Controlled Auto-ignition (CAI) combustion is facilitated in a Ricardo single cylinder engine with a pair of special camshafts, which valve lift and cam profile are modified to trap enough hot residuals. Operation regions and other detailed combustion characteristics of the CAI engine operation are analyzed and compared between pure CAI mode and the CAI mode with assisted spark ignition. The results show that spark ignition can play an important role in controlling CAI combustion ignition in low load boundary region. The low temperature chemical reaction process is shortened and the auto ignition timing is advanced due to the spark discharge. Meantime, lower fuel consumption and cycle-to-cycle variations can be achieved.

With the application of valve timing strategy to inlet and exhaust valves, Homogeneous Charge Compression Ignition (HCCI) combustion was achieved by varying the amount of trapped residuals through negative valve overlap on a Ricardo Hydra four-stroke port fuel injection engine fueled with ethanol. The effect of ethanol on HCCI combustion and emission characteristics at different air-fuel ratios, speeds and valve timings was investigated. The results indicate that HCCI ethanol combustion can be achieved through changing inlet and exhaust valve timings. HCCI ethanol combustion range can be expanded to high speeds and lean burn mixture. Meanwhile, the factors influencing ignition timing and combustion duration are valve timing, lambda and speeds. Moreover, NOx emissions are extremely low under HCCI combustion. The emissions-speed and emissions-lambda relationships are obtained and analyzed.

Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to simultaneously reduce the fuel consumption and nitrogen oxides emissions of gasoline engines. However, narrow operating region in loads and speeds is one of the challenges for the commercial application of CAI combustion to gasoline engines. Therefore, the extension of loads and speeds is an important prerequisite for the commercial application of CAI combustion. The effect of intake charge boosting, charge stratification and spark-assisted ignition on the operating range in CAI mode was reviewed. Stratified flame ignited (SFI) hybrid combustion is one form to achieve CAI combustion under the conditions of highly diluted mixture caused by the flame in the stratified mixture with the help of spark plug.

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.

In Spark Ignition (SI)-Controlled Auto Ignition (CAI) hybrid combustion, the in-cylinder temperature and total mass of dilution charge are usually increased compared to the traditional SI engine in order to achieve and control the auto-ignition combustion, which would in turn lead to the variations of the diluted flame propagation combustion. In this study, the optical measurements were performed to understand the flame characteristics at highly diluted conditions. The results showed that the decrease of the flame propagation speed of rich mixture was less than that of lean mixture at highly diluted conditions. However, the inhomogeneous distribution of residual gas led to asymmetric development of flame propagation. The high temperature, strong dilution and rich mixture created local auto-ignition sites which were located in front of the main flame and gradually merged with the main flame.

In the present study, we developed a reduced TRF-PAH chemical reaction mechanism consisted of iso-octane, n-heptane and toluene as gasoline surrogate fuels for GDI (gasoline direct injection) spark ignition engine combustion simulation. The reduced mechanism consists of 85 species and 232 reactions including 17 species and 40 reactions related to the PAHs (polycyclic aromatic hydrocarbons) formation. The present mechanism was validated for extensive validations with experimental ignition delay times in shock tubes and laminar flame speeds in flat flame adiabatic burner for gasoline/air and TRF/air mixtures under various pressures, temperatures and equivalence ratios related to engine conditions. Good agreement was achieved for most of the measurement. Mole fraction profiles of PAHs for n-heptane flame were also simulated and the experimental trends were reproduced well. The vapor-phase and particulate-bound PAHs existed in GDI engine exhaust were sampled and analyzed by GC-MS.

In this paper, an experimental study was performed to investigate characteristics of flame propagation and knocking combustion of hydrous (10% water content) and anhydrous ethanol at different air/fuel ratios in comparison to RON95 gasoline. Experiments were conducted in a full bore overhead optical access single cylinder port-fuel injection spark-ignition engine. High speed images of total chemiluminescence and OH* emission was recorded together with the in-cylinder pressure, from which the heat release data were derived. The results show that under the stoichiometric condition anhydrous ethanol and wet ethanol with 10% water (E90W10) generated higher IMEP with at an ignition timing slightly retarded from MBT than the gasoline fuel for a fixed throttle position. Under rich and stoichiometric conditions, the knock limited spark timing occurred at 35 CA BTDC whereas both ethanol and E90W10 were free from knocking combustion at the same operating condition.

Using Exhaust Gas Recycling (EGR) on internal combustion engines enables the reduction of emissions with a low or even no cost to the engine efficiency at part-load operation. The charge dilution with EGR can even increase the engine efficiency due to de-throttling and reduction of part load pumping losses. This experimental study proposed the use of late exhaust valve closure (LEVC) to achieve internal EGR (increased residual gas trapping). A naturally aspirated single cylinder direct injection spark ignition engine equipped with four electro-hydraulic actuated valves that enabled full valve timing and lift variation. Eight levels of positive valve overlap (PVO) with LEVC were used at the constant load of 6.0 bar IMEP and the speed of 1500 rpm. The results have shown that later exhaust valve closure (EVC) required greater intake pressures to maintain the engine load due to the higher burned gases content. Hence, lower pumping losses and thus higher indicated efficiency were obtained.

Poppet-valve two-stroke gasoline engines can increase the specific power of their four-stroke counterparts with the same displacement and hence decrease fuel consumption. However, knock may occur at high loads. Therefore, the combustion with stratified lean mixture was proposed to decrease knock tendency and improve combustion stability in a poppet-valve two-stroke direct injection gasoline engine. The effect of intake pressure and split injection on fuel distribution, combustion and knock intensity in lean mixture conditions at high loads was simulated with a three-dimensional computational fluid dynamic software. Simulation results show that with the increase of intake pressure, the average fuel-air equivalent ratio in the cylinder decreases when the second injection ratio was fixed at 70% at a given amount of fuel in a cycle.

Controlled Auto-Ignition (CAI) combustion has been achieved in a production type 4-stroke multi-cylinder gasoline engine. The engine was based on a Ford 1.7L Zetec-SE 16V engine with a compression ratio of 10.3, using substantially standard components modified only in design dimensions to control the gas exchange process in order to significantly increase the trapped residuals. The engine was also equipped with Variable Cam Timing (VCT) on both the intake and exhaust camshafts. It was found that the largely increased trapped residuals alone were sufficient to achieve CAI in this engine and with VCT, a range of loads between 0.5 and 4 bar BMEP and engine speeds between 1000 and 3500 rpm were mapped for CAI fuel consumption and exhaust emissions. The measured CAI results were compared with those of Spark Ignition (SI) combustion in the same engine but with standard camshafts at the same speeds and loads.

An experimental study has been carried out with the end goal of minimizing engine-out methane emissions with Premixed Micro Pilot Combustion (PMPC) in a natural gas-diesel Dual-Fuel™ engine. The test engine used is a heavy-duty single cylinder engine with high pressure common rail diesel injection as well as port fuel injection of natural gas. Multiple variables were examined, including injection timings, exhaust gas recirculation (EGR) percentages, and rail pressure for diesel, conventional Dual-Fuel, and PMPC Dual-Fuel combustion modes. The responses investigated were pressure rise rate, engine-out emissions, heat release and indicated specific fuel consumption. PMPC reduces methane slip when compared to conventional Dual-Fuel and improves emissions and fuel efficiency at the expense of higher cylinder pressure.

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.

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.

Controlled auto-ignition (CAI) combustion and engine performance and emission characteristics have been intensively investigated in a single-cylinder gasoline direct injection (GDI) engine with an air-assisted injector. The CAI combustion was obtained by residual gas trapping. This was achieved by using low-lift short-duration cams and early closing the exhaust valves. Effects of EVC (exhaust valve closure) and IVO (intake valve opening) timings, spark timing, injection timing, coolant temperature, compression ratio, valve lift and duration, on CAI combustion and emissions were investigated experimentally. The results show that the EVC timing, injection timing, compression ratio, valve lift and duration had significant influences on CAI combustion and emissions. Early EVC and injection timing, higher compression ratio and higher valve lift could enhance CAI combustion. IVO timing had minor effect on CAI combustion.

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.