Potential of Reduced Fuel Consumption of Diesel-Electric APUs at Variable Speed in Mobile Applications

Abstract

Auxiliary power units (APUs) are used in mobile applications to provide electrical power until approx. 10 kW. It is state of the art that these generators are driven by a diesel engine at constant speed and are selected according to the expected maximal power needed. These systems have a low efficiency and consequently a high fuel consumption particularly when driven at small loads. The system can yield a higher efficiency for partial load conditions by reducing the rotary speed of the driving diesel engine. The optimum in rotary speed of the diesel engine for different loads is preprogrammed (engine mapping) in the diesel control unit. A frequency converter allows a constant frequency of the electricity output at variable speed of the generator. These higher costs for frequency converter and diesel controller demand especially for mobile applications a proof of efficiency, i.e. a proof of economics, which is shown in this paper. A diesel electric drive train has been mounted on the test rig consisting of a diesel engine, a permanent magnet synchronous generator, a frequency converter and an electric load. The components were analysed individually in a first step to determine the efficiency characteristics. With the individual efficiencies of the components, the total efficiency of the drive train can be calculated in respect to rotary speed and torque. Relevant load profiles where chosen which represent typical duty cycles in stationary and mobile applications. The consumption of the variable speed generator was tested and the control parameters for the diesel engine were optimized using a simulation model. The final control parameters were implemented into the diesel controller at the test rig. The recorded experimental results were compared to the simulation results. The test results proved the precise prediction of fuel consumption by the simulation model. Tests and simulations resulted in a reduction of fuel consumption of about 30% for all of the relevant load profiles compared to the state of the art power units operating at constant speed of revolution. Further fuel saving potential was achieved with a start/stop-function which stops the diesel engine after a determined time period when no power is needed in order to avoid idle operation periods. An economic analysis concludes this study. It was proved that the higher investment costs will be amortized within approx. one year.

The evaluation of developing vehicle technologies on the fuel economy of long-haul trucks

“…Other recent studies have focused on reductions in truck tare weight [17], waste heat recovery [5,[18][19], and limiting idle time [20][21][22]. Light-weight materials are crucial for truck quality, freight efficiency, cost saving and competitiveness [17].…”

“…In particular, Rankine bottoming cycles for recovering waste heat have been adopted by major truck OEMs in achieving more than 50% peak engine efficiency used in SuperTrucks [5][6]. Several options for idle reduction have been developed, including electrical auxiliary power units [20][21] and fuel cell auxiliary power units [22][23][24]. Campbell et al [21] showed that reduction of accessory overdrive and parasitic loading could create a 13%-15% improvement in overall fuel economy.…”

“…The extra-low exhaust temperatures limit waste heat recovery benefits and can impact tailpipe emissions control.Figure 15compares WHR energy recovery of the baseline and long-haul truck integrated with all the developing technologies. The fully integrated vehicle achieves[18][19][20][21][22][23][24][25][26][27][28][29][30] Wh/mile WHR energy recovery providing around 1% fuel economy improvement, roughly 60% less than the 68-96 Wh/mile of the baseline vehicle.…”

An islanded microgrid energy management controller validated by using hardware-in-the-loop emulators

“…A model for the governor of the geothermal unit was also developed. A governor [35], is generally a device designed to maintain the shaft speed of a machine constant, as defined by an energy management system, regardless of the operating conditions. In this case, the governor is also used to implement the droop characteristic of the geothermal generator, as can be observed in Fig.…”

Effects of both blended and pure biodiesel on waste heat recovery potentiality and exhaust emissions of a small CI (compression ignition) engine

“…The knowledge of the energy flows available at different operating conditions, in fact, could be useful for the development of CI engine based cogeneration systems working at different engine speeds and loads [13].…”