Optimum design point to recover maximum possible exhaust heat over the operating range of a small diesel truck using bottoming Rankine cycle

Paper #:
  • 2018-01-1377

  • 2018-04-03
Corporate Average Fuel Economy standards require automakers to raise the average fuel efficiency of new cars and trucks from 24.8 miles per gallon to 54.5 miles per gallon by 2025. Also, the United States Environmental Protection Agency’s greenhouse gas emissions standards are projected to require 163 grams/mile of carbon dioxide (CO2) from 358 grams/mile of CO2 by 2025. This paper focuses on waste heat recovery system, which is an efficient technology to reduce fuel and vehicle CO2 emissions. Wide variations of power of a vehicle make it difficult to design a heat recovery system which can operate optimally at all powers. Usually, a vehicle does not run at rated power and speed all the time. The exhaust temperature from the engine is critical to design a heat recovery system. Higher the temperature higher will be the gain from the waste heat recovery system. However, as power drops the exhaust temperature drops which makes the heat recovery system performs poorly at lower power. In this research, a small truck engine was used to design a heat recovery system to produce additional power. Heat exchangers were used to produce superheated steam which was used to predict additional power using a steam expander. The heat recovery system was designed at the rated power and speed of 42.8 kW and 2600 rpm, respectively. At this design point, 15.41% additional power improvement was achieved resulting 13.35% break specific fuel consumption reduction. Then, the performances of the heat recovery system were evaluated at other powers to cover the span of the vehicle operation. At lower powers, the heat recovery system could produce any additional power due to lower exhaust temperatures. Thereafter, different design points lower than the rated power were chosen to find out optimum design point which covered the usual vehicle operations.
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