VOL. 11, NO. 4, FEBRUARY 2016 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences © 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 2768 INFLUENCE OF THE COMPRESSION RATIO AND IGNITION TIMING ON SINJAI ENGINE PERFORMANCE WITH 50% BIOETHANOL- GASOLINE BLENDED FUEL Bambang Sudarmanta 1 , Bambang Junipitoyo 2 , Ary Bachtiar Krisna Putra 3 and I Nyoman Sutantra 4 1 Fuels and Combustion Engineering Laboratory, Mechanical Engineering Department ITS Sukolilo Surabaya Indonesia 2 Mechanical Engineering Department ITS Sukolilo Surabaya Indonesia 3 Termodynamics Laboratory, Mechanical Engineering Department ITS Sukolilo Surabaya Indonesia 4 Otomotif Laboratory, Mechanical Engineering Department ITS Sukolilo Surabaya Indonesia E-Mail: sudarmanta@me.its.ac.id ABSTRACT Influence of the compression ratio and injection timing on Sinjai engine performance with 50% bioethanol- gasoline blended fuel were investigated on water brake dynamometer. The properties of bioethanol were measured based on American Society for Testing Materials (ASTM) standards. Fuel consumption was measured by the time of fuel consumption per 25 cc of fuel in a measuring glass, whereas combustion air consumption was measured using an air flow meter. The emission parameters, exhaust gas temperature and air fuel ratio were measured using STARGAS exhaust gas analyzer. The compression ratio was increased from 9, 6; 10, 6 to11, 6 dan ignition timing was set for minimum advanced of spark ignition for best torque, MBT with limited by knocking. Ignition timing was adjusted for maximum torque and thermal efficiency. Engine performance testing conducted in a variable speed, starting the engine speed 2000 to 5000 rpm with intervals of an increase of 500 rpm. The engine performance parameters evaluated were torque, brake mean effective pressure, power, specific fuel consumption, thermal efficiency, exhaust gas composition and volumetric efficiency. The results showed that the increase of compression ratios improved engine performance for 50% bioethanol-gasoline blended (E50) fuel throughout all the speed range investigated. The both fuel fuel has same the tendency that the degree of the ignition timing is more advanced due to higher engine speed but the value of degree of ignition timing advanced, from 18 0 BTDC at engine speed 2000 rpm until 26 0 BTDC at engine speed 5000 rpm. The addition of compression ratio requiring retarded ignition timing to avoid detonation. The use of E50 fuel, at the compression ratio is 11.6 can improve brake torque, power and mep respectively by 3, 68%, 4.58% and 3.68% as compared to using pure gasoline at a compression ratio of 9, 6. While the influence of adding compression ratio at the E50 can reduce bsfc by 13, 42 % and increase thermal efficiency by 14, 67 %. Keywords: compression ratio, ignition timing, bioethanol, gasololine, engine performance. INTRODUCTION Developing renewable energy has become an important part of worldwide energy policy to reduce green house gas emissions caused by fossil fuels. Renewable alternative fuels, as defined by the Energy Policy ACT of 1992 (EPACT), include alcohols (biomethanol, bioethanol and others), natural gas, liquified petroleum gas, hydrogen, coal derived liquid fuels, biofuels (include biodiesel, syntesis gas and others), and electricity. These fuels are being used wordwide in a variety of stasioner and mobile applications [1]. They are a major force in the effort to reduce fossil fuels consumption and environmental impact (include harmful pollutans and exhaust emissions) in the transportation sectors. Bioethanol is sustainable fuel that it can be produced from suger cane or other renewable energy sources so it employed most widely. Besides, bioethanol is made up of a group of chemical compounds whose molecules contain a hydroxyl group (OH) that bonded to a carbon atom. The oxygen content of bioethanol fuel favors the further combustion of gasoline [2]. Also, bioethanol is used to increase octane number of gasoline. It can be concluded that using bioethanol–gasoline blended fuels can reduced air pollution and the depletion of gasoline fuels simultaneously. Many researcher were studying the effect of bioethanol fuel on the performance and pollutant emissions of an engine by experimentally [3-6] and artificial neural network [7]. According to these issues, the development of new clean-gasoline engines, such as injection system fueled with bioethanol fuel is important. Because it has the advantages of higher thermal efficiency and power output due to fuel injection than conventional engines [8]. The injection system gasoline engine has also a better transient response, more precise control of the air–fuel ratio, an improvement of fuel economy and a reduction of exhaust emissions. Moreover, the higher compression ratio due to the reduced possibility of knocking, leads to an improvement of the output performance by using gasoline bioetanol blended fuel [9]. Bioethanol has a heating value about 60% lower and higher research octane number than gasoline fuel. These parameters allow higher compression ratio, higher