Fuel economy analysis of part-load variable camshaft timing strategies in two modern small-capacity spark ignition engines

Abstract

 Valve timing strategies are explored at part-load in two small-capacity SI engines  Simplified graphical fuel-economy VCT strategies are provided for the two engines  Engine design specifics exert a profound influence upon optimal valve timings  The theoretical best strategy determines BSFC reduction above 8% for the PFI engine  Maximum BSFC reduction was about 5% for the more efficient GDI platform ABSTRACT Variable Camshaft Timing strategies have been investigated at part-load operating conditions in two 3-cylinder, 1.0-litre, Spark Ignition engines. The two small-size engines are different variants of the same 4-valve/cylinder, pent-roof design platform. The first engine is naturally aspirated, port fuel injection and features high nominal compression ratio of 12:1. The second one is the turbo-charged, direct injection version, featuring lower compression ratio of 10:1. The aim of the investigation has been to identify optimal camshaft timing strategies which maximise engine thermal efficiency through improvements in brake specific fuel consumption at fixed engine load. The results of the investigation show that the two engines demonstrate consistent thermal efficiency response to valve timing changes in the low and mid part-load envelope, up to a load of 4 bar BMEP. At the lower engine loads investigated, reduced intake valve opening advance limits the hot burned gas internal recirculation, while increasingly retarded exhaust valve opening timing favours engine efficiency through greater effective expansion ratio. At mid load (4 bar BMEP), a degree of intake advance becomes beneficial, owing mostly to the associated intake de-throttling. In the upper partload domain, for engine load of 5 bar BMEP and above, the differences between the two engines determine very different efficiency response to the valve timing setting. The lower compression ratio engine continues to benefit from advanced intake valve timing, with a moderate degree of exhaust timing retard, which minimises the exhaust blow-down losses. The higher compression ratio engine is knock-limited, forcing the valve timing strategy towards regions of lower intake advance and lower hot gas recirculation. The theoretical best valve timing strategy determined peak fuel economy improvements in excess of 8% for the port fuel injection engine; the peak improvement was 5% for the more efficient direct injection engine platform.

Investigating the impact of gasoline composition on PN in GDI engines using an improved measurement method

“…Gasoline Direct Injection (GDI) engines offer higher efficiency and lower CO 2 emissions compared to Port-Fuel Injection (PFI) gasoline engines, 1 but with the drawback of higher particulate matter (PM) emission. [2][3][4][5][6] Considering the stringent regulations on particulate mass and particulate number (PN), the need for developing and deepening the knowledge around the complexities of PM formation and measurements in GDI engines is evident.…”

Lumped parameter modeling of hybrid magnetomotive force electromechanical valve actuator

“…The conventional camshaft engines have valve events that can be optimized for finite range at engine development stage to meet engine load and speed requirements [1]. Variable camshaft timing (VCT) mechanism showed 3.5% reduced average fuel consumption on all part-load conditions for port fuel injection [2].…”

Exhaust Tuning of an Internal Combustion Engine by the Combined Effects of Variable Exhaust Pipe Diameter and an Exhaust Valve Timing System

“…A proper variable valve timing system effectively reduces pumping losses and enhances fuel economy as well [12,[23][24][25][26]. Bonatesta et al [27] even mention that an optimized valve timing strategy could improve the peak fuel economy by 5-8% in addition to minimizing exhaust blow-down losses, which subsequently increases the engine power. Studies from Lee et al [28], Li et al [29], Cairns et al [12], Deng et al [30] and Yeom et al [31] also show that adjusting valve timings can reduce NO X emissions, while also achieve high power and efficiency.…”