A simple and efficient mild air hybrid engine concept and its performance analysis

Abstract

In this paper, a simplified and more effective approach to achieve mild air hybrid operation in an engine with split intake ports is presented and its performance is analysed. The regenerative engine braking is achieved by operating the engine as a compressor during vehicle deceleration through the application of a cam profile switching device to one of the intake valves. Compared to the previous concepts, the new approach simplifies the control and allows more compressed air to be captured during the compressor mode operation. A four-cylinder 2.0 l diesel engine has been modelled in Ricardo’s WAVE to operate in an air hybrid engine configuration so that the valve timing optimization during the compressor mode and the expander mode operations could be studied. An air hybrid operation map during the compressor mode is then created, in which the amount of air mass charged (g/cycle) during a deceleration is given as a function of engine braking torque and tank pressure. The other air hybrid operation map for the expander mode operation is generated using a program in MATLAB, which allows the compressed air consumption during each cranking to be determined for a given tank pressure and the number of cylinders. In order to evaluate the potential fuel savings of the mild air hybrid engine technology and the availability of the compressed air for additional usages, a driving cycle simulation program has been developed and applied to a light duty vehicle. The vehicle simulation shows that standard vehicle operation during the New European Driving Cycle consumes 677 g of fuel and the mild air hybrid vehicle uses 631.2 g of fuel, which represents a 6.8% reduction in fuel consumption as a result of the regenerative stop–start operations. In addition, the free compressed air is available to provide instant boost so that a highly downsized engine can be used for further improvement in fuel economy without the loss in performance and greater emissions associated with turbo-lag.

Experimental studies of the air hybrid engine charging operation

“…Therefore, it has confirmed that the use of an intake throttle can be an effective means to controlling the engine braking torque in the air hybrid engine operations. This provides the basis of the engine response map of the compressor mode operation comprising engine braking torque values as a function of throttle positions, which has been used for the vehicle driving cycle analysis [10,11]. Table 4 shows an engine response map which summarises the tank pressure and the intake throttle valve opening as functions of the flow rate (g/cycle) of air mass charged for the engine speed range between 1000 and 2000 rpm.…”

“…This provides the basis of the engine response map of the compressor mode operation comprising engine braking torque values as a function of throttle positions, which has been used for the vehicle driving cycle analysis. 10,11…”

“…This provides the basis of the engine response map of the compressor mode operation comprising engine braking torque values as a function of throttle positions, which has been used for the vehicle driving cycle analysis. 10,11 Table 4 shows an engine response map which summarises the tank pressure and the intake throttle valve opening as functions of the flow rate (g/cycle) of air mass charged for the engine speed range between 1000 and 2000 r/min. It shows the engine braking imep rather than engine braking torque for compressor mode because of the larger flywheel and higher frictional losses than the production engine.…”

Effect of piston shape design on the scavenging performance and mixture preparation in a two-stroke boosted uniflow scavenged direct injection gasoline engine

“…The variable valve actuation (VVA) system could be applied to optimise the opening profiles of exhaust valves for maximum scavenging performance. An additional air transfer valve was included for the air-hybrid operation, 38 which could transfer the brake energy into high-pressure compressed air to be stored and then used for stop-start and boost operations. The application of late DI after the closure of scavenge ports and exhaust valves could avoid fuel short-circuiting in BUSDIG engine.…”

Study of a hybrid pneumatic-combustion engine under steady-state and transient conditions for transport application

“…The simulation showed that the pneumatic hybridisation could recover about 10% of total energy under different conditions. Lee et al 23–25 studied a cost-effective mild hybrid pneumatic engine concept for buses and commercial vehicles. The simulation showed that the fuel mass consumed during the New European Driving Cycle (NEDC) was 677 g for a standard vehicle and 631.2 g for a hybrid pneumatic vehicle, indicating a fuel saving effect of 6.8%.…”