Work Extraction Efficiency in a Series Hybrid Opposed Piston Engine

Drallmeier, Joseph A.; Hofmann, Heath; Middleton, Richard H.; Siegel, Jason B.; Stefanopoulou, Anna G.; Salvi, Ashwin

doi:10.4271/2021-01-1242

Cited by 3 publications

(4 citation statements)

References 8 publications

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“…10,11 The introduction and preliminary evaluation of a hybrid design utilizing electric machines attached directly to the two crankshafts of the OP engine to extract mechanical work from combustion and convert it to electricity was previously performed by the authors. 12 This work extends the previous study by evaluating the unique operational opportunity and challenges of using electric motors to independently control the engine crankshafts' motion. The objective is to optimize the engine's thermodynamic cycle as well as the efficiency with which electrical energy is extracted from the system to maximize the brake system output for a fixed energy input.…”

Section: Introductionmentioning

confidence: 58%

“…The coefficient C is used to scale the friction losses of the motor and is set to 0.038 here by fitting the P loss to the motor efficiency map for the electric machines used by the authors previously. 12 Any losses from the engine are included in the engine torque for a given setpoint and thus the motor torque through the torque balance on each crankshaft. It is important to note here that the motor losses are included as a power loss rather than an efficiency applied to the torque and speed term as T * ω * η motor sgn ( T ) .…”

Section: Optimal Control Problemmentioning

confidence: 99%

“…The impact of the work extraction efficiency, however, has been shown to be a critical component in the overall system efficiency. 12…”

Section: Introductionmentioning

confidence: 99%

“…The impact of the work extraction efficiency, however, has been shown to be a critical component in the overall system efficiency. 12 In this paper, we develop a procedure to optimize the motion of each crankshaft in an opposed piston engine utilizing compression ignition to maximize brake output power, including the mechanical to electrical conversion efficiency for extracting the rotational work from the crankshafts. The conversion efficiency in this case is the electric motor efficiency for the motor attached to each crankshaft and is shown to be a dominant factor in the brake system efficiency.…”

Section: Introductionmentioning

confidence: 99%

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Optimizing the fuel efficiency of an opposed piston engine for electric power generation

Drallmeier

Middleton

Siegel

2022

International Journal of Engine Research

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This paper investigates the optimal crankshaft motion for an opposed piston (OP) engine in a novel hybrid architecture to maximize fuel efficiency. The OP engine was selected for this work due to its inherent thermodynamic benefits and the balanced nature of the engine which can achieve downsizing through reducing the number of cylinders rather than the individual cylinder volume. The typical geartrain required on an OP engine was exchanged for two electric motors, reducing friction loss and decoupling the crankshafts. Using the motors to control the crankshaft motion profiles, this architecture introduces capabilities to dynamically vary compression ratio, combustion volume, and scavenging dynamics. To leverage these opportunities, an optimization scheme was developed utilizing nonlinear optimization of a 0-D model to compute the crankshaft motion profile that maximizes the work generated by the system. This optimization was then iteratively coupled with a high fidelity model which supplies the cylinder flow boundary conditions. This iterative approach reduces the model complexity used in the optimal control problem (OCP) while capturing the gas exchange dynamics critical to the 2-stroke cycle of the OP engine. By using the rate of change of motor torque as the input to the OCP, the torque fluctuation in a single cycle can be limited to ensure tracking feasibility. The results show crankshaft velocity slows during the compression stroke and conversely accelerates during the expansion stroke, reducing the peak motor torque required for control and thus reducing the motor losses. The extended residence time at top dead center, however, leads to an increase in heat transfer, illustrating the trade-off between the work extraction efficiency and the indicated engine efficiency.

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Section: Introductionmentioning

confidence: 58%