Developing a diesel exhaust heat recovery system : final design report

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Firmansyah, Fajar
Pawluk, Michael
Price, Trevor
Temple, Travis
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This report describes the design process used to develop a diesel exhaust heat recovery system for a New Flyer 40 ft bus and proposes a design that meets the principle design constraints. A heat recovery system is required to replace the auxiliary heater currently used in New Flyer’s 40 ft bus. The auxiliary heater is used to supplement in cabin heat and maintain engine temperature. The diesel fired auxiliary heater emits unfiltered exhaust gas and lowers fuel economy. These by-products of its function are environmentally damaging and un-economical. In order to replace the function of the auxiliary heater with a heat recovery system, several constraints and performance specifications, identified by New Flyer, need to be respected. Specifically, the heat recovery system must produce 23 kW of heat and impose no more than 3386 Pa of back pressure onto the exhaust system. Also, it should not measure more that 812.8 mm long, 304.8 mm in diameter and weigh no more than 26 kg. Additionally, the new system should cost less than $3000. These space and weight constraints imposed by New Flyer, limited the variety and size of possible designs that would meet the performance expectations stated above. Furthermore, adhering to industry heat exchanger design standards, such as TEMA (Tubular Exchange Manufacturing Association), imposed additional restrictions on the design possibilities. In order to address these design constraints while achieving the required performance, numerical and optimization software, such as MATLAB, EXCEL and SOLIDWORKS were used to optimize and check possible heat exchanger geometries that met both TEMA standards and the size constraints imposed by New Flyer. In addition to providing a detailed analysis of the heat exchanger, details of integrating it into the bus’s exhaust and coolant system are provided in this report. A cost analysis, including the cost of manufacturing the heat exchanger, installation and the addition of tubing and valves required to control the flow of coolant and exhaust gas through the new system. Based on our analysis, we have designed a single pass, shell and tube heat exchanger that meets the performance specifications but is outside of the space constraints. The exchanger should perform at approximately 30% efficiency; providing 24 kW at peak torque and an additional back pressure of 2.72 kPa at maximum power. The overall length of the design is 766.6 mm which is within the space constraints; however the overall diameter is 336.4 mm which is beyond the height constraint by 32.4 mm. The weight of the heat exchanger is 100.5 kg; therefore, it does not meet the weight constraint. However, the overall cost of our design is $2957.40 which is within budget.
diesel, exhaust, heat, recovery, system, New Flyer Industries