Contents lists available at Mapta Publishing Group Mapta Journal of Mechanical and Industrial Engineering (MJMIE) journal homepage: http://maptapublishing.com/index.php/mjmie Vol. 2, No. 2, August, 2018 ISSN: 2517-4258 1 Optimization of Fuel Consumption of a SI Engine Using Variable Valve Timing and Variable Length Intake Manifold Techniques Mohammad Keshavarz a , Mehdi Keshavarz b,* a Department of Mechanical Engineering, Arsanjan Branch, Islamic Azad University, Arsanjan, Iran b Faculty of Mechanical Engineering, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr, Iran Article Info Abstract Article history: Received May 14 th , 2018 Revised Jul 9 th , 2018 Accepted Jul 24 th , 2018 According to the world crisis about fuel consumption and environmental concerns regarding toxic emissions of internal combustion engines, the engines with higher efficiency and lower fuel consumption have been a topic of research in last decades. In this study, variable valve timing (VVT) and variable length intake manifold (VLIM) techniques are used to optimize the fuel consumption of an SI engine. At first, all components of engine are modeled in GT-POWER and a comparison with experimental results is performed to confirm the accuracy of the model. Then, the discrete-gird algorithm is employed to optimize the parameters in GT-POWER. The results obtained indicate that optimal valve timing and intake manifold length significantly reduces brake specific fuel consumption (BSFC). Keyword: Variable valve timing Variable length intake manifold GT-POWER Fuel consumption Discrete-grid algorithm 1. Introduction The universal regulations governing the control of green-house gas emissions are now being tightened so that vehicle manufacturers have to satisfy these constraints. The reduction of engine fuel consumption becomes a primary requirement to meet current and future emission legislations [1]. For this purpose, several methods such as fast combustion, lean burn, variable valve timing and gasoline direct injection have been suggested in the literature. Variable valve timing is one of the most efficient methods which not only reduces fuel consumption and engine emissions but also, solves low end torque problem. In automotive applications, the variable valve timing was first developed by Fiat in late 1960 [2]. Considering the ability of the system, it was soon used by other companies like Honda, General Motors, Ford and other automobile manufacturers. Liguang et al. [3] examined intake and exhaust valve timing effects on spark ignition engines. They experimentally investigated the effect of these two factors on power, torque, fuel consumption and the HC emissions. Bohac et al. [4] studied the effect of variable exhaust valve opening (EVO) and exhaust valve closing (EVC) on HC emissions reduction. They studied the effect of different EVO and EVC timings under steady-state and start-up conditions, and concluded that the early EVO could be helpful for engine HC emission reduction in steady-state conditions but not in start-up condition. Shayler [5] experimentally investigated the effects of intake and exhaust valves timing on remaining output gases. He concluded that timing of intake and exhaust valves will have considerable influence on the extent of fuel and fresh air entrance to the combustion chamber. Leroy et al. [6] conducted a series of research into controlling intake air path in an engine having a variable valve system without EGR. They considered internal EGR effect in engines having variable valve systems and studied their effects on reducing fuel consumption and emissions as well as negative effects of increased internal EGR on torque and air-fuel ratio. They presented a new control way by which beneficial effects of variable valve system would be added and its negative effects would be reduced. Wu et al. [7] optimized valve timing of a gasoline engine using a neural network algorithm. The result of this study was to reach optimal timing by using neural network in a variable valve system engine. Therefore a mathematical model of the target engine has been made, * Corresponding author: mehdi.k1001@gmail.com  This is an open access article under the CC-BY license (https://creativecommons.org/licenses/by/4.0/). © Authors retain all copyrights.