Zhongchang Liu

Structure and Parameters Optimization of Organic Rankine Cycle System for Natural Gas Compressor Exhaust Gas Energy Recovery

In the paper, the structure and working principle of free piston based organic rankine cycle (ORC) exhaust gas energy recovery system have been presented in detail. A GT-Power software based prototype model has been established in order to find out the effects of different parameters. Comparisons under different thermo parameters of heated and cold work material have been analyzed thoroughly. Simulation results show that the thermo parameters of heated work material are very sensitive to net heat efficiency.

Simulation of EGR Stratification on Timing-Sequential Regionalized Diesel Combustion

In this paper, the influences of EGR distribution on timing-sequential regionalized diesel combustion characters and emissions have been investigated numerically. Timing-sequential regionalized diesel combustion described in previous paper is realized by post injection and proper in-cylinder chemical atmosphere transport to keep post injection fuel injecting to high oxygen concentration region. Cases with EGR stratification have similar heat release rate character compare to uniform EGR case while lower soot emissions and identical NO emissions as local EGR rate equal to uniform case, similarly, lower NO emissions and identical soot emissions as EGR mass equal to uniform case. Axial and radical EGR stratification that defined artificially in cylinder under the condition of 1,650 r/min and 50 % load have been numerically analysed by commercial STAR-CD code. It is indicated that both axial and radical distribution of EGR stratification make NO and soot emissions decrease simultaneously, however, radical EGR distribution works better. NO emissions decrease while soot emissions keep constant under the case of EGR stratification with post injection using main injection timing advance and higher local EGR rate; it is also found that cyclic net work per cylinder is improved at some extent. Intake port shape and swirl rate also have been investigated to analyse in-cylinder gradient of EGR distribution to achieve EGR stratification. EGR gas distributes by gradient in cylinder as air and air-EGR mixture flow through two intake valve that connected to tangential and spiral intake port respectively.

Numeric investigation of EGR and post-injection diesel emissions

In this paper, the effects of post-injection with EGR (exhaust gas recirculation) on diesel emissions are investigated to provide fundamental basis for controlling of EGR and post-injection on diesel. Various EGR rate with or without post-injection keeping the same total injection fuel under the speed of 1650r/min and 50% load conditions were simulated. It was found that soot emissions could keep constant as EGR rate increasing with post-injection compared to without post-injection conditions under low EGR rate (lower than 5%), at the same time NO emissions effectively decreased about 5%. However, as EGR rate is going to increase, soot emissions worsen sharply. Different dwell of Main and Post injection has irregular effects of NO and soot emissions under higher EGR rate of 14.7%, at the same time. NO and soot emissions changed regularly as main and post injection dwell increasing. It was also found that as Main injection timing advancing, the indicated thermal efficiency and soot emissions under high EGR rate were improved. And with 20% EGR, main injection timing advanced to 20° CA BTDC, the indicated thermal efficiency and soot emissions are more perfect than non-EGR.

Research and Development of Heavy-Duty NG Engine and its Key Technologies of Combustion

In this paper, A heavy-duty NG engine and its electronic controlled system were developed. combustion stability, in–cylinder flow, burning rate and hazardous emissions were further investigated to develop optimized combustion control technologies for efficient and clean combustion on this engine. The electronic controlled system and NG supply system were designed in the condition of maintaining the universal parts of based diesel engine as many as possible. The combustion and emissions of NG engine were investigated by means of experiment and numerical simulation with the commercial 3D-CFD-tool STAR-CD. The in-cylinder flow and burning rate of NG engine were studied. Special-shaped combustion chamber was used to change the flow state. The results show that the engine thermal efficiency increases by 2 % compared with the original engine while using the cross-type rapid combustion chamber under 1450r/min,100 % load operating condition. Effect of three kinds of dilution methods on combustion and emissions performance from lean burn NG engine was investigated. These dilution methods include air dilution, stoichiometric combustion with EGR, and double dilution (extra air and EGR). The results show that double dilution method is superior to other methods no matter considering from fuel economy or NOx emissions.

Effects of EGR rate and excess air ratio on the combustion characteristics of compressed natural gas engine

The influence of EGR (exhaust gas recirculation) rate and excess air ratio (λ) on the combustion and emissions of a twofold dilution compressed natural gas (CNG) engine CA6SE3-21E4N were investigated experimentally to solve the limited decreasing-ability on NOx emissions with air dilution. The results show that as EGR rate and λ increase, the peak of cylinder pressure and heat release rate decrease and delay, the heat release centroids and the start of combustion move backward, the main combustion duration becomes longer and then the flame propagation velocity slows down. The cyclic variations intensify versus the EGR rate and λ increase. With smaller λ than that of air dilution under equivalent NOx emission levels, the twofold dilution makes the engine operating more stably. Considering the trade-off between NOx emissions and fuel economy, values as optimal control point can be obtained under 1750r/min, 75% load conditions, namely, λ is 1.35, EGR rate is 7%.