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An applicable approach to mitigate pressure rise rate in an HCCI engine with negative valve overlap. Applied energy 257.

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ABSTARCTThe paper presents the numerical analysis of the drag force generated on the body of a sports car, based on the CFD method in the Ansys Fluent program. The three-dimensional model of the vehicle was taken from an open CAD database. Based on this, a computational grid was developed, boundary conditions and a turbulence model were defined. As a result of the calculations, the pressure distribution on the individual body parts and the velocity distribution in selected cross sections were obtained. In the next part of the research, the simulation results are used to optimize the shape of the bodywork of different passenger vehicles in order to reduce the generated drag force.

Homogeneous charge compression ignition concepts despite high efficiency and ultra-low nitrous oxides emissions, suffer from week controllability and load range limited by excessive pressure rise rates. In the present work, controlled auto-ignition is achieved via direct injection of gasoline into the exhaust gasses recompressed during negative valve overlap phase. Single cylinder engine experiments are designed to explore the potential of additional late post injection strategies for pressure rise rate and peak pressure suppressing. For two mixture strengths, fuel distribution is varied between 3 gasoline injection events. In-depth combustion analysis is supported by emission measurement results. Increasing the amount of gasoline, post-injected during the main compression event, was proven to be an effective measure for reducing pressure rise rates, with over 50% reduction potential. The regulation capability however, is limited by typical tread-offs between stratified and homogenous fuelling concepts. Using post injection strategy results in decreased hydrocarbon emissions, but causes rapid increase in carbon monoxide and particulate matter emissions. Nitrous oxide increase rate is dependent on mixture strength with significantly higher sensitivities during lean operation.

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This study investigates combustion and emission characteristics of a contemporary single-cylinder compression ignition engine fuelled with diesel, fatty acid methyl esters (FAME) and hydrotreated vegetable oil (HVO). These two drop-in fuels have an increasing share in automotive supply chains, yet have substantially different physical and auto-ignition properties. HVO has a lower viscosity and higher cetane number, and FAME has contrary characteristics. These parameters heavily affect mixture formation and the following combustion process, causing that the engine pre-optimized to one fuel option can provide deteriorated performance and excess emissions if another sustainable option is applied. To investigate the scale of this problem, injection pressure sweeps were performed around the stock, low NOX and low PM engine calibration utilizing split fuel injection. The results showed that FAME and HVO prefer lower injection pressures than diesel fuel, with the benefits of simultaneous reduction of all emission indicators compared to DF. Additionally, reduction of injection pressure from 80 MPa to 60 MPa for biodiesels at low engine load resulted in improved brake thermal efficiency by 1 percentage point, due to reduced parasitic losses in the common rail system.

One of the most important requirements in the design of diesel combustion systems is to reduce emissions of harmful chemical compounds contained in exhaust gases. Solution to this problem is sought by the use of advanced engine injection systems and accurate control of mixture formation inside a cylinder via split fuel injection. The differences in physical characteristics between traditional and alternative fuels can affect fuel metering, especially at short injection durations. Thus, the aim of the current study was to identify dynamic flow parameters of the Common Rail injector with the use of different fuels. The study involved Diesel available in retail and biodiesel fuel obtained by methyl esterification of fatty acids. Measurements were performed on a test stand designed for determination of injectors and injection pumps characteristics. Studies were carried out changing the following parameters: injection pressure in the range of 30-180 MPa, injection time in the range of 200-1600 microseconds. Each fuel was tested at temperature 40 and 60°C. The obtained test results showed that injection of different fuels provided variable amounts of fuel injected at short injection durations, which can affect mixture formation process as well as combustion. Effect of the dose of the injected fuel has a viscosity of used fuel.