BSFC Investigation Using Variable Valve Timing in a Heavy Duty Diesel Engine

摘要

Variable valve actuation in heavy duty diesel engines is not well documented, because of diesel engine feature, such as, unthrottled air handling, which gives little room to improve pumping loss; a very high compression ratio, which makes the clearance between the piston and valve small at the top dead center. In order to avoid strike the piston while maximizing the valve movement scope, different strategies are adopted in this paper: (1) While exhaust valve closing is fixed, exhaust valve opening is changed; (2) While exhaust valve closing is fixed, late exhaust valve opening: (3) While inlet valve opening is fixed, inlet valve closing is changed; (4) Delayed Inlet valve and exhaust valve openings and closings; (5) Changing exhaust valve timing; (6) changing inlet valve timing; (7) Changing both inlet and exhaust timing, will be used. In order to see how much fuel efficiency could be improved in addition to EGR (Exhaust Gas Recirculation) and VGT (Variable Geometry Turbo-charger), EGR and VGT are fully controlled in a closed-loop. This paper examines fuel consumption improvement at different speeds and torques. Finally we could see 6% BSFC benefit could be achieved at some map points. The reason of this benefit is that fixed valve lift engine makes a compromise between high speed engine performance and low speed fuel economy and variable valve timing optimizes valve timing at each engine torque and speed. This paper will also investigate the issues regarding late inlet valve closing, which has been addressed in [4] and [7]. This paper will investigate late inlet valve closing in a different angle and different view point.