Development of 1.5L Dedicated Hybrid Engine with 42.6% Brake Thermal Efficiency

To achieve higher brake thermal efficiency (BTE) and improve vehicle economy, the new development of dedicated hybrid engine (DHE), adopting the Atkinson or Miller cycle, has been becoming the current development trends. A base 1.5L natural aspiration (NA) engine with deep Atkinson cycle has been developed for dedicated hybrid vehicle application, which can achieve the highest BTE of 41.19%. In order to achieve higher BTE, several potential technologies which are easy for mass production application have been studied progressively, such as, higher compression ratio (CR), optimized exhaust gas recirculation (EGR) pick point, lower EGR temperature, higher EGR rate, higher RON number fuels, heat transfer reduction by polishing valve head, light boost, lower viscosity oil. The results show the combined technology application can achieve the highest engine BTE of 42.59%. This paper provides the studied technical routine and the achieved benefits step by step.

Research of the efficiency of using the Miller cycle of an internal combustion engine

The article is devoted to the study of the possibilities of improving the technical and economic indicators of an internal combustion engine (ICE) through the use of the Miller cycle with a shortened intake. A review of scientific works on the use of the Atkinson cycle and Miller cycle in an internal combustion engine is carried out. A comparative analysis of theoretical cycles: Otto cycle, Atkinson cycle and Miller cycle is carried out. Calculated studies of the influence of the expansion ratio and the pressure increase ratio on the efficiency of the Atkinson cycle have been carried out. The ratios are presented that allow using the Miller cycle with a short inlet to obtain the same theoretical efficiency of the cycle as that of the Atkinson cycle. At the same time, the implementation of the Miller cycle in a real engine design significantly exceeds the possibilities of using the Atkinson cycle. The results of the study showed that the use of the Miller cycle with a shortened intake is preferable, but it must necessarily increase the compression ratio and intake pressure through the use of boost. On the example of real data of the main parameters of the cycle, it is shown that the use of the theoretical Miller cycle can provide a significant up to 12.2% increase in the efficiency of the cycle compared to the Otto cycle. The ratios, conditions and recommendations are presented that allow the effective use of the Miller cycle with a shortened intake in a real engine design.

Performance Optimizations with Single-, Bi-, Tri-, and Quadru-Objective for Irreversible Atkinson Cycle with Nonlinear Variation of Working Fluid’s Specific Heat

Considering nonlinear variation of working fluid’s specific heat with its temperature, finite-time thermodynamic theory is applied to analyze and optimize the characteristics of an irreversible Atkinson cycle. Through numerical calculations, performance relationships between cycle dimensionless power density versus compression ratio and dimensionless power density versus thermal efficiency are obtained, respectively. When the design parameters take certain specific values, the performance differences of reversible, endoreversible and irreversible Atkinson cycles are compared. The maximum specific volume ratio, maximum pressure ratio, and thermal efficiency under the conditions of the maximum power output and maximum power density are compared. Based on NSGA-II, the single-, bi-, tri-, and quadru-objective optimizations are performed when the compression ratio is used as the optimization variable, and the cycle dimensionless power output, thermal efficiency, dimensionless ecological function, and dimensionless power density are used as the optimization objectives. The deviation indexes are obtained based on LINMAP, TOPSIS, and Shannon entropy solutions under different combinations of optimization objectives. By comparing the deviation indexes of bi-, tri- and quadru-objective optimization and the deviation indexes of single-objective optimizations based on maximum power output, maximum thermal efficiency, maximum ecological function and maximum power density, it is found that the deviation indexes of multi-objective optimization are smaller, and the solution of multi-objective optimization is desirable. The comparison results show that when the LINMAP solution is optimized with the dimensionless power output, thermal efficiency, and dimensionless power density as the objective functions, the deviation index is 0.1247, and this optimization objective combination is the most ideal.

A Theoretical Study on the Thermodynamic Cycle of Concept Engine with Miller Cycle

The Atkinson cycle, where expansion ratio is higher than the compression ratio, is one of the methods used to improve thermal efficiency of engines. Miller improved the Atkinson cycle by controlling the intake- or exhaust-valve closing timing, a technique which is called the Miller cycle. The Otto–Miller cycle can improve thermal efficiency and reduce NOx emission by reducing compression work; however, it must compensate for the compression pressure and maintain the intake air mass through an effective compression ratio or turbocharge. Hence, we performed thermodynamic cycle analysis with changes in the intake-valve closing timing for the Otto–Miller cycle and evaluated the engine performance and Miller timing through the resulting problems and solutions. When only the compression ratio was compensated, the theoretical thermal efficiency of the Otto–Miller cycle improved by approximately 18.8% compared to that of the Otto cycle. In terms of thermal efficiency, it is more advantageous to compensate only the compression ratio; however, when considering the output of the engine, it is advantageous to also compensate the boost pressure to maintain the intake air mass flow rate.

Effects of intake valve opening duration on performance optimization of an Atkinson cycle engine under part load

A comprehensive analysis of the intake valve opening duration (IVOD) effects on the performance of an Atkinson cycle engine is conducted in this work using numerical simulation and experimental validation. Through one-dimensional simulation, the relationship between the range of IVOD and the compression ratios is firstly investigated under the constraint of compression pressure. Two representative IVOD, 295 and 314°CA, are then respectively applied to the performance simulation and experiment of a practical Atkinson cycle engine. The simulation shows the combination of a late intake valve opening timing (IVO) angle and a late exhaust valve opening timing (EVO) angle is profitable for improving the fuel economy under part load operating conditions (i.e. 2000 rpm@2 bar and 3000 rpm@3 bar). The experimental results present the Atkinson cycle engine under both IVOD scenarios considerably improves the brake specific fuel consumption (BSFC) and reduces the pumping mean effective pressure (PMEP) compared to those of the original Otto cycle engine. Meanwhile, the comparison between two IVOD scenarios show that the shorter IVOD leads to an improvement of indicated thermal efficiency, especially at lower load. Considering fuel economy, a shorter IVOD is more favorable at part load for the Atkinson cycle engine. Two main contributions of this work are to numerically quantify the IVOD range for the Atkinson cycle engine under part load, and to experimentally validate the effectiveness of simulation. The findings of this work are expected to support the design of Atkinson cycle engines and provide a guideline of IVOD optimization under part load.