Modeling of Compressed Air Hybrid Operation for a Heavy Duty Diesel Engine

Abstract

Internal combustion engines can be modified to operate regenerative braking cycles by using compressed air power. This paper presents a particular air hybridization design from among many possible configurations. The engine cycles are enabled by a highly flexible engine valvetrain, which actuates engine valves to generate desired torque with optimal efficiency. A lumped parameter model is developed first to investigate the cylinder-tank mass and energy interaction based on thermodynamic relationships and engine piston kinematics. Special consideration is given to the engine valve timing and air flow. A high fidelity, detailed model using the commercially available GT-Power software is developed for a commercial 10.8 liter heavy-duty diesel engine with a 280 liter air tank in order to capture the effects of engine friction, heat transfer, gas dynamics, etc. The model is used to develop optimal valve timing for engine control. The established engine maps are incorporated into the ADVISOR vehicle simulation package to evaluate the potential fuel economy improvement for a refuse truck under a variety of driving cycles. Depending on the particular driving cycle, the simulation has shown a potential 4% – 18% fuel economy improvement over the truck equipped with the conventional baseline diesel engine.

Working Characteristics of Variable Intake Valve in Compressed Air Engine

“…Because the throttling effect from the intake or exhaust valve accounts for energy losses, valve flow is critical to the CAE. Valve flow is considered as one-dimensional isentropic flow [ 18 , 19 ].…”

Research on a pneumatic hybrid engine with regenerative braking and compressed-air-assisted cranking

“…The modelled improvements in the fuel economy of a passenger car were shown to be about 64% and 12% in the city driving cycle and the highway driving cycle respectively. In addition, Kang et al 13 and Wang et al 14 applied the air hybrid to heavy-duty diesel engines and refuse trucks using three-way valves, compressor bypass valves and hydraulic valves. A concept with three-way valves and bypass valves was also proposed by Basbous et al 15 From a perspective of engine downsizing and supercharging, Dönitz et al 7,16 set up a two-cylinder pneumatic hybrid engine test bench; this was equipped with a dedicated electrohydraulic charge valve on each cylinder which replaced one of the exhaust valves.…”