CAI combustion and the factors affecting it were intensively investigated in a single cylinder, air-assisted gasoline direct injection engine. CAI was achieved by means of residual gas trapping by utilising low-lift short duration camshafts and early closing of the exhaust valves. The effects of EVC (Exhaust Valve Closure) and IVO (Inlet Valve opening) timings, spark timing, single and split injection timings, coolant temperature, compression ratio, cam lift and duration on exhaust emissions and CAI operation were investigated experimentally. Engine speed throughout the course of the experiments, was varied from 1200rpm to 2400rpm and the air/fuel ratio was altered from stoichiometric to the misfire limit. The results show that the EVC timing, compression ratio, cam lift and duration had significant influences on CAI combustion and emissions. Early EVC when combined with higher compression ratio and higher cam lift, enhance CAI combustion operation and stability. IVO timing had minor effect on CAI combustion while spark timing hardly affects CAI operation as soon as fully-developed CAI conditions were established. Coolant temperature was revealed to have substantial impact on CAI combustion when the coolant temperature was below 65C. The results also show the importance of injection timing. Early injection gave faster and more stable combustion, less HC and CO emissions, but more prone to knocking combustion and higher NOx emissions. Furthermore, CAI operation range could considerably be extended with injection during the recompression process. Late injection led to slower and unstable combustion, higher HC and CO emissions but lower combustion noise and NOx emissions. Split injection gave even further extension of CAI range in both stoichiometric and lean mixture operations. All the above clearly suggest, that optimising injection timing and using split injection is an effective way to control and extend CAI operation in a direct injection gasoline engine.

This study investigates the effects of a split injection strategy on combustion performance and exhaust emissions in a high speed direct injection optical diesel engine. The investigation is focused on the effects of injection timing, quantity, and the dwell angle between the injections using commercially available diesel fuel. Three different split injection strategies including 50:50, 30:70, and 70:30 have been investigated. Additionally, the effect of total injected fuel quantity using total fuel quantities of 10 mm3 and 20 mm3 has been investigated. Moreover, the effect of variable and fixed dwell angle in split injections has been examined for five different values between 5o CA and 25o CA in the case of variable and 10o CA for the fixed dwell timing. The last parameter investigated was the injection timing, nine injection timings have been tested for each of the strategies. A Ricardo Hydra single cylinder optical engine running at 1500 rpm was used in this investigation. Conventional methods such as direct in-cylinder pressure measurements and heat release rate analysis have been employed. In addition, optical techniques such as high speed video imaging and two-colour have been applied, aimed at in depth analysis of the effects of the aforementioned parameters on engine performance and emissions. Furthermore, a significant amount of effort was devoted to the development and application of the Laser Induced Excipex Fluorescence (LIEF) technique so that simultaneous fuel liquid and fuel vapour distribution could be visualised. This investigation concludes that split injection strategies have the potential to reduce diesel exhaust emissions while maintaining a good level of fuel economy, provided that injection timings and the dwell angle between injections are appropriately selected. Further investigations are required in order to examine the effect of split injection under different engine operating conditions and speeds. In addition, the effect of alternative fuels must be considered. Moreover, the application of LIEF technique for quantitative fuel vapour concentration measurement should be considered through further optimisation of the LIEF system and careful calibration experiments.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22552号 / エネ博第403号 / 新制||エネ||77(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)教授 石山 拓二, 教授 川那辺 洋, 教授 今谷 勝次 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

Political, environmental and marketing factors mean there is a global requirement to produce vehicles with improved fuel economy and reduced emissions. This thesis shows that the gasoline direct injection (GDI) engine will continue to form a significant portion of the automotive propulsion market in the short to medium term. However, to reach future targets continuous development and optimisation of these engines is essential. The introduction to this thesis discusses the role some of the key aspects of GDI engine design have on overall engine efficiency. The fuel spray is shown to be a key contributor to this, as it is a primary driver in the fuel/air mixing process, and therefore intrinsically linked to the combustion efficiency.

Diesel Engine has been the most powerful and relevant source of power in the automobile industryfor decades due to their excellent performance, efficiency and power. On the contrary, there arenumerous environmental issues of the diesel engines hampering the environment. It has been agreat challenge for the researchers and scientists to minimize these issues. In the recent years, severalstrategies have been introduced to eradicate the emissions of the diesel engines. Among them,Partially Premixed Combustion (PPC) is one of the most emerging and reliable strategies. PPC is acompression ignited combustion process in which ignition delay is controlled. PPC is intended toendow with better combustion with low soot and NOx emission.The engine used in the present study is a single-cylinder research engine, installed in Aalto UniversityInternal Combustion Engine Laboratory with the bore diameter of 200 mm. The thesis presentsthe validation of the measurement data with the simulated cases followed by the study of the sprayimpingement and fuel vapor mixing in PPC mode for different injection timing. A detailed study ofthe correlation of early injection with the fuel vapor distribution and wall impingement has beenmade.The simulations are carried out with the commercial CFD software STAR CD. Different injectionparameters have been considered and taken into an account to lower the wall impingement and toproduce better air-fuel mixing with the purpose of good combustion and reduction of the emissions.The result of the penetration length of the spray and the fuel vapor distribution for different earlyinjection cases have been illustrated in the study. Comparisons of different thermodynamic propertiesand spray analysis for different injection timing have been very clearly illustrated to get insightof effect of early injection. The parameters like injection timing, injection period, injection pressure,inclusion angle of the spray have an influence the combustion process in PPC mode. Extensivestudy has been made for each of these parameters to better understand their effects in the combustionprocess. Different split injection profiles have been implemented for the study of better fuelvapor distribution in the combustion chamber.The final part of the thesis includes the study of the combustion and implementation of EGR tocontrol the temperature so as to get more prolonged ignition delay to accompany the PPC strategyfor standard piston top and deep bowl piston top. With the injection optimization and implementationof EGR, NOx has been reduced by around 44%, CO by 60% and Soot by 66% in the standardpiston top. The piston optimization resulted in more promising result with 58% reduction in NOx,55% reduction in CO and 67% reduction in Soot. In both cases the percentage of fuel burnt wasincreased by around 8%.

Diesel engine emissions of oxides of nitrogen and particulate matter can be reduced simultaneously through the use of high levels of exhaust gas recirculation (EGR) to achieve low temperature combustion (LTC). Although the potential benefits of diesel LTC are clear, the main challenges to its practical implementation are the requirement of EGR levels that can exceed 60%, high fuel consumption, and high unburned hydrocarbon and carbon monoxide emissions. These limit the application of LTC to medium loads. In order to implement the LTC strategy in a passenger vehicle engine, a transition to conventional diesel operation is required to satisfy the expected high load demands on the engine. The investigation presented in this thesis was therefore aimed at improving the viability of the high-EGR LTC strategy for steady-state and transient operation. An experimental investigation was carried out on a single cylinder high-speed direct injection diesel engine. This thesis presents research on engine in-cylinder performance and engine-out gaseous and particulate emissions at operating conditions (i.e. EGR rate, intake pressure, fuel quantity, injection pressure) likely to be encountered by an engine during transient and steady-state operation. At selected operating points, further investigation in terms of in-cylinder spray and combustion visualization, flame temperature and soot concentration measurements provided deeper insight into the combustion and emissions phenomena. Increased intake pressure at single injection high-EGR LTC operation was investigated as a strategy to reduce the emissions of partial combustion by-products and to improve fuel economy. The higher intake pressure, although effective in reducing partial combustion by-products emissions and improving fuel economy, increased the EGR requirement to achieve LTC. A split fuel injection strategy with advanced injection timing on the other hand was effective in reducing the EGR requirement for LTC from 62% with single injection to 52% with split injections at 120 kPa (absolute) intake pressure. Unburned hydrocarbon emissions and fuel economy were particularly sensitive to intake oxygen mass fraction, and injection and dwell timings with the split injection strategy. In-cylinder soot formation and oxidation mechanisms with the split injection strategy were found to be significantly different from the single injection high-EGR LTC case. Transient simulation of an engine during combustion mode transition identified engine operating parameters on a cycle-by-cycle basis. Steady-state investigation of these test conditions provided significant insight into the combustion conditions and their effect on emissions and performance. The results from this thesis demonstrated the importance of optimizing both the air handling system performance and the fuel injection system during engine transients. The increased emissions and impaired performance due to slow response of the EGR and turbocharger systems during transitions to and from LTC modes can in part be mitigated through split injections optimized for the specific transient point. This provides a clear direction for engine developers to pursue in optimizing engine calibration when running with LTC-conventional diesel dual-mode strategies.