New Variable valve timing strategy based on using auxiliary valve having variable timing (VVT) is used in this study. The valve is driven by a new variable valve timing mechanism constructed for this purpose. The auxiliary valve acts as an exhaust valve and the experiments and simulation model are carried out at different loads. The results show that engine performance is improved at full load and worsens at part loads. The study proves that using an auxiliary exhaust valve having variable timing is not recommended in engines applications. NOMENCLATURE A c p , c v D _ Mass fraction, position coordinate Greek Symbols Crank position angle (degree) Combustion duration (degree) Boltzman constant Density (kg/m 3) Equivalence ratio Supscripts Burn Unburn wall Superscripts Derivative with time (d/dt) Molar quantity
A new variable valve timing strategy based on using an auxiliary valve having a variable timing (VVT) is used in this study. The valve is driven by a new VVT mechanism achieving valve duration and opening angle variations. The auxiliary valve acts as intake valve. Experiments and simulation models are carried out at different loads. The results show improvements in brake thermal efficiency, fuel consumption, volumetric efficiency, residual gas fraction and engine emissions over the whole range of load. Swirl and tumble ratios are decreased. Ahmed, S.A. et al. 468 load), 0.75 kW (1/2 load) and 0.4 kW (1/4 load). At each load the engine parameters under considerations are: brake power, mass flow rates of air, fuel and fresh charge, volumetric efficiency, brake thermal efficiency and bsfc. The one-dimensional simulation model which is described in [11], predicts residual gas fraction, CO concentration based on dry moles, NOx and HC concentrations. Table 1 shows the engine performance parameters at the loads under consideration.
Electrohydraulicservos exhibit nonlinear behavior whenever subjected to dynamic inputs due to the presence of several significant nonlineari^ies in the servovalve and hydraulic motor. Some mechanical nonlinearities are often responsible for performance limitations as expressed by speed of response, accuracy and stob^li^y^ This paper deal with the dynamic characteristics of electrohydraulic velocity servos in order to throw more light on the complicated role play^d by stick-slip friction of the actuator.
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