Experimental and numerical study of a two-stroke poppet valve engine fuelled with gasoline and ethanol

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThe restrictions imposed by CO2 emission standards in Europe and many countries have promoted the development of more efficient spark ignition engines. The reduced swept volume and number of cylinders of four-stroke engines has significantly improved fuel economy by means of lower pumping and friction losses. This approach, known as engine downsizing, has demonstrated its potential of reducing fuel consumption on its own as well as applied to hybrid vehicles where a low weight engine is desired. However, aggressive engine downsizing is currently constrained by thermal and mechanical stresses and knocking combustion. In order to overcome these limitations, the present work evaluates the application of a conventional poppet valve direct injection engine into the two-stroke cycle. Two-stroke engines have the ability to produce higher power with reduced swept volume and less weight than four-stroke engines thanks to the doubled firing frequency. These advantages, although, are sometimes offset by poorer emissions resulted from fuel short-circuiting; lower thermal efficiency resulted from short expansion process; and reduced engine durability due to lubrication issues. Therefore, in this research the four-stroke engine architecture was employed so these shortcomings could be addressed by the use of direct fuel injection, variable valve actuation and a wet crankcase, respectively. The burnt gases were scavenged during a long valve overlap by means of boosted air supplied by an external compressor. An electrohydraulic fully-variable valve train enabled the optimisation of the gas exchange process in a variety of engine operating conditions. The air-fuel mixture formation was evaluated through computational fluid dynamic simulations and correlated to experimental tests. In addition, the engine operation with ethanol was assessed in a wide range of engine loads and speeds. Finally, the engine performance, combustion process, air-fuel mixing and gas exchange results were presented, discussed and contextualised with current four-stroke engines. Keywords: Two-stroke poppet valve engine; gasoline and ethanol direct injection; engine downsizing; supercharged two-stroke cycle.Brazilian council for scientific and technological development (CNPq - Brasil

High load performance and combustion analysis of a four-valve direct injection gasoline engine running in the two-stroke cycle

With the introduction of CO2 emissions legislation or fuel economy standards in Europe and many countries, significant effort is being made to improve spark ignition gasoline engines because of their dominant market share in passenger cars and potential for better fuel economy. Amongst several approaches, the engine downsizing technology has been adopted by the automotive companies as one of the most effective methods to reduce fuel consumption of gasoline engines. However, aggressive engine downsizing is constrained by excessive thermal and mechanical loads as well as knocking combustion and low speed pre-ignition (also known as super-knock). In order to overcome such difficulties, a gasoline direct injection single cylinder engine was modified to run under the two-stroke cycle by operating the intake and exhaust valves around bottom dead centre (BDC) at every crankshaft revolution. The combustion products were scavenged by means of a reversed tumble flow of compressed air during the positive valve overlap period at BDC. The engine output was determined by the charging and trapping efficiencies, which were directly influenced by the intake and exhaust valve timings and boost pressures. In this research a valve timing optimisation study was performed using a fully flexible valve train unit, where the intake and exhaust valve timings were advanced and retarded independently at several speeds and loads. A supercharger was used to vary the load by increasing the intake pressure. The effects of valve timing and boost pressure in this two-stroke poppet valve engine were investigated by a detailed analysis of the gas exchange process and combustion heat release. Gaseous and smoke emissions were measured and analysed. The results confirmed that the two-stroke cycle operation enabled the indicated mean effective pressure to reach 1.2MPa (equivalent to 2.4MPa in a four-stroke cycle) with an in-cylinder pressure below 7MPa at an engine speed as low as 800rpm. The engine operation was limited by scavenging inefficiencies and short time available for proper air-fuel mixing at high speeds using the current fuel injector. The large amounts of hot residual gas trapped induced controlled auto-ignition combustion at high speeds, and thus the abrupt heat release limited higher loads.The Brazilian council for scientific and technological development (CNPq – Brasil

Consumo de combustível e emissões de poluentes em um motor Diesel convertido a etanol para geração térmica de energia elétrica

Nos esforços globais para a minimização nas emissões de gases do efeito estufa e redução da pegada de carbono, combustíveis renováveis têm sido extensivamente utilizados em substituição aos combustíveis fósseis nos motores de combustão interna. Particularmente para geração de energia elétrica local, motores diesel são os mais utilizados devido à elevada eficiência térmica e a robustez, se comparado a motores de ignição por centelha. Entretanto, estes sistemas apresentam elevados níveis de emissões de óxido de nitrogênio (NOx) e material particulado, trazendo sérias consequências para o meio ambiente. Assim, esta pesquisa combina simulação computacional e resultados experimentais da conversão de um motor diesel para a operação com etanol, sendo sua utilização na geração de energia elétrica. Como este combustível renovável é largamente produzido no Brasil utilizando a cana-de-açúcar, acaba por possuir seu custo reduzido em especial próximo à produtores e refinarias. Dados experimentais foram utilizados na validação do modelo computacional unidimensional desenvolvido para a conversão, onde resultados foram analisados para a comparação de ambos combustíveis. Análises econômicas para diferentes condições de carga forneceram informações de custos operacionais em locais próximos às fontes de produção de etanol. Os resultados apontam as vantagens no uso do combustível renovável para a geração de energia elétrica, como o custo reduzido e a menor emissão de NOx ao longo de toda a gama de operação.</p

Performance and economic analysis of a direct injection spark ignition engine fueled with wet ethanol

The use of wet ethanol with higher water content than the conventionally used in internal combustion engines can reduce fuel production costs due to lower energy expense during the distillation phase. However, during its combustion the extra water content may result in the deterioration of fuel conversion efficiency and therefore a global energy evaluation should be considered. This research investigated the operation of a single cylinder direct injected spark ignition engine running with gasoline, anhydrous ethanol and several wet ethanol compositions (5-20% of water-in-ethanol volumetric content) under stoichiometric and lean air/fuel ratios. Two part load conditions of 3.1 bar and 6.1 bar indicated mean effective pressure were evaluated at 1500 RPM. The impacts of increased water-in-ethanol content and lean operation on combustion and emissions were discussed. Higher water content affected the heat release rate, which increased the combustion duration and initial flame development phase. Lower nitrogen oxides emissions could be achieved with higher water-content ethanol at the expense of higher unburned hydrocarbon emission. An analysis of wet ethanol energy production costs and engine operation conditions was carried out. The lean engine operation with 10% (v/v) water-in-ethanol fuel showed global energy savings around 31% compared to anhydrous ethanol at stoichiometric conditions.The Brazilian Council for Scientific and Technological Development (CNPq – Brasil) supported the PhD studies of Mr. Lanzanova and Mr. Dalla Nora at Brunel University London

Experimental analysis of ethanol dual-fuel combustion in a heavy-duty diesel engine: An optimisation at low load

Conventional diesel combustion produces harmful exhaust emissions which adversely affect the air quality if not controlled by in-cylinder measures and exhaust aftertreatment systems. Dual-fuel combustion can potentially reduce the formation of nitrogen oxides (NOx) and soot which are characteristic of diesel diffusion flame. The in-cylinder blending of different fuels to control the charge reactivity allows for lower local equivalence ratios and temperatures. The use of ethanol, an oxygenated biofuel with high knock resistance and high latent heat of vaporisation, increases the reactivity gradient. In addition, renewable biofuels can provide a sustainable alternative to petroleum-based fuels as well as reduce greenhouse gas emissions. However, ethanol-diesel dual-fuel combustion suffers from poor engine efficiency at low load due to incomplete combustion. Therefore, experimental studies were carried out at 1200. rpm and 0.615. MPa indicated mean effective pressure on a heavy-duty diesel engine. Fuel delivery was in the form of port fuel injection of ethanol and common rail direct injection of diesel. The objective was to improve combustion efficiency, maximise ethanol substitution, and minimise NOx and soot emissions. Ethanol energy fractions up to 69% were explored in conjunction with the effect of different diesel injection strategies on combustion, emissions, and efficiency. Optimisation tests were performed for the optimum fuelling and diesel injection strategy. The resulting effects of exhaust gas recirculation, intake air pressure, and rail pressure were investigated. The optimised combustion of ethanol ignited by split diesel injections resulted in higher net indicated efficiency when compared to diesel-only operation. For the best emissions case, NOx and soot emissions were reduced by 65% and 29%, respectively. Aftertreatment requirements that are generally associated with cost and fuel economy penalties can be minimised. Combustion efficiency of 98% was achieved at the expense of higher NOx emissions.The Brazilian Federal Agency for Support and Evaluation of Postgraduate Education (CAPES) and the National Council for Scientific and Technological Development (CNPq), Mr. Pedrozo and Mr. Dalla Nora at Brunel University Londo