내연기관의 폐열회수를 이용한 동력전환 장치의 효율 향상에 관한 연구

Abstract

본 논문은 내연기관에서 동력전환 후 버려지는 배기가스를 통해 회수한 폐열을 동력으로 전환하는 장치인 팽창기의 효율 향상에 관한 연구로 Rankine Cycle을 이론적 배경으로 하고 있다. 3.3ℓ가솔린 엔진이 탑재된 승용차량의 배기가스를 열원으로 하고 120km/hr 조건을 설계 기준점으로 하여 24.6kW의 배기에너지 중에 촉매의 활성화 온도에 필요한 열을 제외하고 열교환기를 통해 회수율 65%로 16kW의 열을 회수한 뒤, 팽창기 효율을 70%로 가정하면 1.9kW의 동력을 엔진으로 전달할 수 있으며, 이때의 동력전달효율은 95%를 적용하였다. 이는 설계점에서 대상차량의 연비를 7% 개선할 수 있는 동력이다. 배기가스에서 회수한 열에너지를 동력으로 전환하기 위해 대상차량의 배기에너지 양과 작동유체의 온도에 적합한 사판식 팽창기를 선정하였으며, 300℃, 25bar의 작동유체인 스팀을 통해 목표 출력을 엔진에 전달할 수 있도록 팽창비가 10이고 실린더의 개수가 8개인 팽창기를 설계하였다. 팽창기의 마찰손실과 누설손실을 최소화하여 목표로 하는 70%의 팽창기 효율을 달성하기 위해 밸브의 형상과 구조를 단순화 하여 동력손실을 최소화 하고, 누설을 저감하기 위한 기밀 구조를 적용하였으며, 열팽창을 고려한 피스톤의 설계 및 적절한 윤활성능을 가질 수 있도록 윤활시스템을 구성하고 릴리프 밸브를 적용하여 높은 압력에 의해 윤활유가 팽창실로 역류하는 것을 방지하였다. 팽창기의 성능실험을 위해서 팽창기를 일정회전수로 구동하기 위한 동력계, 축 동력을 측정하기 위한 토크미터, 열원에 해당하는 열매체 보일러, 보일러와 과열기에 해당하는 열교환기, 팽창기를 통해 배출된 작동유체를 응축시키기 위한 응축기, 작동유체를 고압의 상태로 이송하기 위한 냉매펌프를 각각 구성하였다. 단계별로 총 3개의 시제품을 제작하여 실험을 진행하였고, 실험결과 설계점에서 초기 이론 출력의 36% 수준의 마찰력이 측정되었으나 씰 개선을 통해 이론 출력의 16% 수준까지 마찰손실을 개선을 하였다. 팽창기 출력은 2.2kW로 해석결과인 2.1kW를 상회하는 출력을 얻을 수 있었고, 밸브의 개선을 통해 초기 42% 수준의 체적효율에서 60%로 체적효율을 개선하였으며, 설계점에서 초기 30%의 팽창기 효율에서 최종적으로 67%의 팽창기 효율을 달성하여 목표 효율인 70%에 근접하는 결과를 얻을 수 있었다.|This paper is a study of improvement in expander efficiency, a device that converts waste heat recovery through exhaust gas wasted after the conversion of power from the internal combustion engine, and sets forth the Rankine cycle as its theoretic background. The exhaust gas of the passenger cars built in with 3.3ℓ gasoline engine is the heat source, and setting 120km/hr condition as the designing point, and recovering 16KW heat with heat recovery rate being 65% through the heat exchanger except the heat needed for the temperature activating the catalytic converter from 24.6kW exhaust energy as the designing point, and then assuming the expander efficiency as 70%, 1.9kW of power can be transmitted to the engine, and the power transmission efficiency at this time was 95%. This is the power that can improve the fuel economy of the test vehicle by 7% from the designing point. In order to convert the heat energy recovered from the exhaust gas into the power, swash plate expander appropriate for the amount of exhaust energy and temperature of the working fluid has been selected for the test vehicle, and through the steam, which is a working fluid of 300℃, 25bar, an expander with its expansion ratio being 10 and the number of cylinders being 8 so that it can transmit the objective output to the engine was designed. In order to achieve 70% of expander efficiency, which is its objective, while minimizing the friction loss and leakage loss of the expander, the valve's shape and structure were simplified, with power loss reaching its minimum, while applying confidential structure to reduce the leakage, and a lubrication system was composed that can hold appropriate lubricant performance and design of a piston that considered the heat expansion with the relief valve applied in composition of lubrication system so that the lubricant might not flow backward to the expansion chamber with high pressure. In order to test the performance of the expander, it was composed of a dynamometer to be drived with regular rotations, a torque-meter to measure the power of axis, thermal oil heater boiler which is the heat source, a heat exchanger that falls under the boiler and superheater, a condenser to condense the working fluid emitted through the expander and a cooler pump to transport the working fluid to high pressure. 3 prototypes were produced and experimented as a whole by each step, and as a result of the experiment, frictional force, which is approximately 36% of the initial theoretical output from the designing point, was improved by 16% level of the theoretical output through seal improvement. The output of the expander was 2.2kW, which is over 2.1kW -the interpretative result,- and through the improvement of the valve, the volumetric efficiency of about 42% at the early stage was improved to 60%, and the result was close to 70% of goal efficiency by finally accomplishing 67% of the expander efficiency from 30% at the beginning of the designing point.; This paper is a study of improvement in expander efficiency, a device that converts waste heat recovery through exhaust gas wasted after the conversion of power from the internal combustion engine, and sets forth the Rankine cycle as its theoretic background. The exhaust gas of the passenger cars built in with 3.3ℓ gasoline engine is the heat source, and setting 120km/hr condition as the designing point, and recovering 16KW heat with heat recovery rate being 65% through the heat exchanger except the heat needed for the temperature activating the catalytic converter from 24.6kW exhaust energy as the designing point, and then assuming the expander efficiency as 70%, 1.9kW of power can be transmitted to the engine, and the power transmission efficiency at this time was 95%. This is the power that can improve the fuel economy of the test vehicle by 7% from the designing point. In order to convert the heat energy recovered from the exhaust gas into the power, swash plate expander appropriate for the amount of exhaust energy and temperature of the working fluid has been selected for the test vehicle, and through the steam, which is a working fluid of 300℃, 25bar, an expander with its expansion ratio being 10 and the number of cylinders being 8 so that it can transmit the objective output to the engine was designed. In order to achieve 70% of expander efficiency, which is its objective, while minimizing the friction loss and leakage loss of the expander, the valve's shape and structure were simplified, with power loss reaching its minimum, while applying confidential structure to reduce the leakage, and a lubrication system was composed that can hold appropriate lubricant performance and design of a piston that considered the heat expansion with the relief valve applied in composition of lubrication system so that the lubricant might not flow backward to the expansion chamber with high pressure. In order to test the performance of the expander, it was composed of a dynamometer to be drived with regular rotations, a torque-meter to measure the power of axis, thermal oil heater boiler which is the heat source, a heat exchanger that falls under the boiler and superheater, a condenser to condense the working fluid emitted through the expander and a cooler pump to transport the working fluid to high pressure. 3 prototypes were produced and experimented as a whole by each step, and as a result of the experiment, frictional force, which is approximately 36% of the initial theoretical output from the designing point, was improved by 16% level of the theoretical output through seal improvement. The output of the expander was 2.2kW, which is over 2.1kW -the interpretative result,- and through the improvement of the valve, the volumetric efficiency of about 42% at the early stage was improved to 60%, and the result was close to 70% of goal efficiency by finally accomplishing 67% of the expander efficiency from 30% at the beginning of the designing point.