Interactions between charge conditioning, knock and spark-ignition engine architecture

There are currently many factors motivating car manufacturers to reduce the tailpipe CO2 emissions from their products. One of the major routes to achieving reduced CO2 emissions in spark-ignition 4-stroke engines is to ‘downsize’ the swept volume which, among other advantages, reduces the proportion of fuel energy expended on pumping losses. The full-load performance deficit caused by reducing the swept volume of the engine is normally recovered by pressure charging. One of the limits to pressure charging is combustion knock, which is the unintended autoignition of the last portion of gas to burn in the combustion chamber after combustion has been initiated. This thesis presents results from investigations into a number of methods for suppressing knock, including (1) tests where the density of the intake air is closely controlled and the effect of charge air temperature is isolated, (2) where the latent heat of vaporization of a fuel is used to reduce the outlet temperature of a supercharger, and (3) where the engine architecture is configured to minimize exhaust gas residual carryover to the benefit of stronger knock resistance. Extensive comparison of this resulting engine architecture is made with published data on other strategies to reduce the effect of the knock limit on engine performance and efficiency. Several such strategies, including cooled EGR, were then investigated to see how much further engine efficiency (in terms of brake specific fuel consumption) could be improved if they are adopted on an engine architecture which has already been configured with best knock limit performance in mind. Within the limits tested, it was found that if the charge air density is fixed then the relationship between knock-limited spark advance and air temperature is linear. This methodology has not been found in the literature and is believed to be unique, with important ramifications for the design of future spark-ignition engine charging systems. It was also found that through a combination of an optimized direct-injection combustion system, an exhaust manifold integrated into the cylinder head, and a 3-cylinder configuration, an engine with extremely high full-load thermal efficiency can be created. This is because these characteristics are all synergistic. Against the baseline of such an engine, other technologies such as excess air operation and the use of cooled EGR are shown to offer little improvement. When operating a pressure-charged engine on alcohol fuel, it was found that there exists a maximum proportion of fuel that can be introduced before the supercharger beyond which there is no benefit to charge temperature reduction by introducing more. Strategies for reducing the amount of time when such a system operates were developed in order to minimize difficulties in applying such a strategy to a practical road vehicle. Finally, a new strategy for beneficially employing the latent heat of vaporization of the fuel in engines employing cooled EGR by injecting a proportion of the fuel charge directly into the EGR gas is proposed. This novel approach arose from the findings of the research into pre-supercharger fuel introduction and cooled EGR

The Role of Low Carbon Alcohol Fuels in Advanced Combustion

The production of alcohol fuels from bioderived feedstocks and the performance of next generation stratified low temperature combustion (LTC) modes for internal combustion engines are two research areas that have recently undergone rapid growth independently. Now, there is a need to bridge these two fields and identify the optimal combustion strategy for these low-carbon and carbon-neutral alcohol fuels as well as potential synergies. The large set of next generation stratified LTC modes are generalized into two groups based on how the heat release process proceeds in the compositionally stratified combustion chamber: lean-to-rich or rich-to-lean burn stratified combustion. It was found that the C1-C4 alcohol fuels are prime candidates to enable lean-to-rich burn stratified combustion based on their high cooling potentials and lack of cool flame reactivity (pre-ignition reactions). Previous experimental work by the author showed that a lean-to-rich burn stratified combustion mode, thermally stratified compression ignition (TSCI), can be enabled using a split injection of wet ethanol to gain control over the heat release process. The current work further investigates TSCI with wet ethanol experimentally on a diesel engine architecture, finding that the effectiveness of TSCI’s heat release control strategy is not affected by the use of external, cooled exhaust gas recirculation or intake boost. Further, it was shown that the effectiveness of TSCI’s heat release control strategy is highly coupled to the hardware used. Specifically, an injector whose spray targets high local heat transfer regions in the cylinder during the compression stroke is more effective at controlling the heat release process than an injector whose spray targets the adiabatic core. Additionally, a piston whose geometry allows regions with high compression stroke heat transfer to be distinct from the adiabatic core, such as a re-entrant bowl piston, will also increase the effectiveness of TSCI’s heat release control strategy. Using a split injection strategy to enable TSCI is not the only way to increase natural thermal stratification and control the heat release process. In this work, high-load LTC is experimentally enabled with wet ethanol on a light-duty gasoline engine architecture by employing a side-mounted, single hole injector with a relatively low injection pressure in a fairly quiescent combustion chamber. The low mixing propensity of this architecture results in a self-sustaining increase of thermal stratification that allows the high-load limit of LTC to be oxygen limited rather than noise limited. Following the experimental work with TSCI with wet ethanol, the LTC performance of seven bio-synthesizable C1-C4 alcohol fuels (methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and sec-butanol) is experimentally characterized, showing that with the exception of n-butanol, the LTC performance of these fuels are similar, implying the remaining six fuels could form an equivalence class of fuels for LTC. To further explore this possibility, two previously proposed LTC fuel metrics are considered: critical compression ratio, a metric that describes the ignition propensity of a fuel in LTC, and normalized φ-sensitivity, a metric that describes how the local ignition delay time responds to a change in φ. The critical compression ratio, experimentally measured on a cooperative fuel research (CFR) engine, was shown to accurately predict the HCCI ignition propensity of the alcohol fuels near the critical compression ratio operating conditions. Similarly, the normalized φ-sensitivity showed the potential to predict the effectiveness of a fuel to control the heat release process of LTC using small amounts of in-cylinder stratification. The normalized φ-sensitivity could then serve as a blending benchmark for multi-alcohol water fuel blends

Alternative Fuels for Transportation

Exploring how to counteract the world's energy insecurity and environmental pollution, this volume covers the production methods, properties, storage, engine tests, system modification, transportation and distribution, economics, safety aspects, applications, and material compatibility of alternative fuels. The esteemed editor highlights the importance of moving toward alternative fuels and the problems and environmental impact of depending on petroleum products. Each self-contained chapter focuses on a particular fuel source, including vegetable oils, biodiesel, methanol, ethanol, dimethyl ether, liquefied petroleum gas, natural gas, hydrogen, electric, fuel cells, and fuel from nonfood crops

Federal Register

Daily publication of the U.S. Office of the Federal Register contains rules and regulations, proposed legislation and rule changes, and other notices, including "Presidential proclamations and Executive Orders, Federal agency documents having general applicability and legal effect, documents required to be published by act of Congress, and other Federal agency documents of public interest" (p. ii). Table of Contents starts on page iii