Biodiesel Fueled Engine Generator With Heat Recovery: Comparing Biodiesel to Diesel Performance

Abstract

Carnegie Mellon University’s departments of Architecture and Mechanical Engineering have designed and installed a biodiesel fueled engine-generator with heat recovery equipment to supply electric and thermal power to an office building on campus, the Intelligent Workplace (IW). The installation was completed in early September 2007, and was commissioned through April of 2008 with standard off-road low sulfur Diesel (LSD) fuel. Additional baseline testing was conducted with LSD until October 2008, when the transition was made to a 100% soybean oil based biodiesel. The turbocharged diesel engine-generator set is operated in parallel with the local electric utility and the campus steam grid. The system is capable of generating 25 kW of electric power while providing 18 kW of thermal power in the form of steam from an exhaust gas boiler and 19 kW in the form of heated water from the engine coolant. The steam is delivered to a double-effect Lithium-Bromide (Li-Br) absorption chiller, which supplies chilled water to the IW for space cooling in the summer or hot water for space heating in the winter. Furthermore, the steam can be delivered to the campus steam grid during the fall and spring when neither heating nor cooling is required in the IW. The thermal energy recovered from the coolant provides hot water for space heating in the winter, and for regenerating a solid desiccant dehumidification ventilation system in summer. All relevant temperatures, pressures, and flows for these systems are monitored via a building automation system. Pressure versus time versus crank angle measurements are recorded in each cylinder of the engine. Emissions of nitric oxide (NO), nitrogen dioxide (NO2), Particulate Matter (PM), carbon monoxide (CO) and carbon dioxide (CO2) are also monitored. The performance testing thus far indicates that biodiesel fuel performs just as well as Diesel fuel in the CHP system, providing similar amounts of electrical and thermal energy at the similar temperatures and flows at a similar overall efficiency. As expected, the engine consumes more biodiesel fuel due to the lower energy density of biodiesel fuel compared to LSD. Upon completion of the system performance testing with different types of biodiesel fuel, the operation of the engine generator with its heat recovery components will be integrated with the other HVAC components of the IW including a parabolic trough solar thermal driven Li-Br absorption chiller, a solid desiccant dehumidification ventilation system, and multiple types of fan coils and radiant heating and cooling devices. This integrated energy supply system is expected to reduce the IW’s primary energy consumption by half in addition to the 75% site energy savings already realized by architectural features as compared to the average US office space.