Kyung-Wook Choi

Effect of the heat exchanger in the waste heat recovery system on a gasoline engine performance

In this paper, the effects of increasing the back pressure on the engine performance by using heat exchangers mounted in the exhaust line to recover waste heat from the engine exhaust are described. An experimental study was conducted with two different types of heat exchanger, namely shell-and-tube-type heat exchangers and fin-and tube-type heat exchangers. The heat exchanger increased the resistance of the engine exhaust through the exhaust line, and the engine back pressure increased to 16 kPa, which led to an increase in the brake specific fuel consumption by up to 3% depending on the operating conditions. The back pressure adversely affected the performance of the automotive engine combined with the Rankine cycle and thus caused the overall thermal efficiency of the system to deteriorate. Consequently, if the back-pressure effect was taken into account, the contribution of recovering heat from the engine exhaust to the improvement in the system efficiency was lower than expected.

A Methodology of an Automotive Engine Cooling Using a Phase Change Material

The size of a cooling inventory is generally designed based on which size can endure the excessive heat load situations that occur sporadically. As a result, cooling systems are often too large for most normal driving modes. There have been numerous efforts to downsize the automotive engine cooling system using novel concepts and strategies (e.g. THEMIS cooling system, CoolMaster, UltimateCooling). However, in terms of the system design, preserving the passive cooling strategy may be simpler and more practical than implementing any major changes. Vetrovec (2008) proposed the use of a heat accumulator that has a phase change material (PCM) within the automotive cooling system. Excessive heat generated during severe operating conditions is stored in the heat accumulator, and it is dissipated during periods of low heat load. The heat dissipation capacity of the radiator and the amount of coolant in the cooling system are normally designed such that the system can sustain itself at peak heat load during acceleration and hill ascents in hot summer periods. Therefore, the unnecessarily large cooling inventory creates an overloaded vehicle which increases the fuel consumption rate. A heat accumulator which averages out the peak heat loads can reduce the entire cooling system remarkably in terms of both its volume and weight. Effective cooling in automobiles is beneficial in reducing harmful emissions as well as improving fuel economy. A simulation was conducted to validate the feasibility of using a novel cooling strategy that utilized the heat load averaging capabilities of a phase change material (PCM). Three prototypes were designed: full size, down sized, and a down sized prototype with a heat accumulator containing the PCM inside. When the full size of the cooling inventory was downsized by 30%, this smaller design failed to dissipate the peak heat load and consequently led to a significant increase in the coolant temperature, around 25 °C greater than that in the full size system. However, the peak heat load was successfully averaged out in the downsized system with a heat accumulator. Experimental study is also on-going to validate the simulation results and find more suitable PCM for the application.Copyright

A Study on the Way to Improve Efficiency of a Waste Heat Recovery System for an Automotive Engine

In recent, there are tremendous efforts to apply co-generation concept in automobile to improve its thermal efficiency. The co-generation is basically a simple Rankine Cycle that uses the waste heat from the engine exhaust and coolant for heat source. In spite of developed nano technology and advance material science, the bulky co-generation system is still a big concern in automotive application. Therefore, the system should be effectively designed not to add much weight on the vehicle, but the capacity of the waste heat recovery should be still large. With such a goal in mind, the system thermal efficiency was investigated in terms of the system operation condition and working fluid. This paper provides a direction for the optimal design of the automotive co-generation system.

Parametric study of the effects of the design factors on the performance of a heat recovery system obtained from an exhaust gas in a gasoline engine

A parametric study was conducted to determine the optimum operating conditions of a waste heat recovery system obtained from the exhaust gas. An analysis of the Rankine cycle was also performed with respect to the changes in the evaporation pressure and the mass flow rate of the working fluid, which have a significant influence on the performance of a heat recovery system. The analysis conditions in this study were selected on the basis of the mass production of an actual waste heat recovery system attached to a real engine exhaust manifold, and the energy flow obtained from gasoline engines was analysed using the first and second laws of thermodynamics. A model for analysing the heat exchanger was also developed using the experimental data on heat transfer between the actual exhaust gas and the working fluid. Based on this model, a cycle analysis of the waste heat recovery system was conducted through one-dimensional simulation. The optimum operating conditions and waste heat recovery system performance were determined from the analytical results. In addition, the potential of the heat recovery system was evaluated by investigating the brake specific fuel consumption of a gasoline engine equipped with a waste heat recovery system.

A novel EGR system to improve engine performance of a diesel engine

A recent focus on automotive researches is to reduce CO2 emission due to stringent regulation. Auto makers has been dealing such regulations with either applying novel combustion strategies or utilizing alternative fuels for IC engines. In addition, low emission vehicles such as HEV and FCEV have developed to reduce emission and fuel consumption. Of IC engines, diesel engine having a higher thermal efficiency compared to gasoline engine has an advantage of a low CO2 emission. In this study, various effects of cooled EGR on diesel engine performances, emission and combustion characteristics were investigated. A separate cooling circuit in combination with additional heat exchangers were installed to control temperatures of EGR gas and charged air independently. As the EGR gas temperature was decreased, PM and NOx emission and BSFC were substantially reduced. However, the cooled EGR was found to increase THC and CO emissions.

A Novel Cooling Strategy for a Diesel Engine to Improve Engine Power Efficiency and Emissions

Stringent regulations on CO2 emission causing greenhouse effect have drawn attention of automotive manufacturers to the diesel engine. The trend is to increase the engine power per liter, and research are being carried out to satisfy the regulation. In this paper, a new cooling strategy was proposed to control coolant more efficiently. Before carrying out a new cooling strategy, preliminary tests on the cooling components were performed. Measurement of metal temperature of the engine indicates that the conventional cooling system was designed inappropriately large to endure at high load conditions. Therefore several strategies were adapted to optimize the size of the conventional cooling system using an Electric Water Pump (EWP), Electric Valve (EV) and low temperature EGR cooler. A cooling system in a 2.7 liter Direct Injection Diesel Engine was modified for the purpose of this study, and the strategies were tested in a stationary test bench. As a result, emission and fuel consumption decreased in high coolant temperature and low coolant flow. Warm-up period in which THC and CO emissions were significant was shortened by controlling the coolant flow paths using EVs. An essential component in a diesel engine is an Exhaust gas recirculation (EGR) system that decreases combustion temperature and oxygen concentration resulting in a substantial reduction of NOx emission. The coolant circulates through the EGR cooler so that the EGR gas temperature could be dropped down, resulting in more efficient combustion. New cooling strategies were found to improve emissions and fuel economy of engines.Copyright