Factors Limiting the Improvement in Thermal Efficiency of S. I. Engine at Higher Compression Ratio

1987 ◽  
Author(s):  
Shigeo Muranaka ◽  
Yasuo Takagi ◽  
Tokuhei Ishida
Keyword(s):  
Compression Ratio ◽  
Thermal Efficiency

scholarly journals A Theoretical Study on the Thermodynamic Cycle of Concept Engine with Miller Cycle

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 1051
Author(s):  
Jungmo Oh ◽  
Kichol Noh ◽  
Changhee Lee
Keyword(s):  
Compression Ratio ◽  
Thermal Efficiency ◽  
Engine Performance ◽  
Thermodynamic Cycle ◽  
Expansion Ratio ◽  
Boost Pressure ◽  
Miller Cycle ◽  
Compression Pressure ◽  
Air Mass ◽  
Atkinson Cycle

The Atkinson cycle, where expansion ratio is higher than the compression ratio, is one of the methods used to improve thermal efficiency of engines. Miller improved the Atkinson cycle by controlling the intake- or exhaust-valve closing timing, a technique which is called the Miller cycle. The Otto–Miller cycle can improve thermal efficiency and reduce NOx emission by reducing compression work; however, it must compensate for the compression pressure and maintain the intake air mass through an effective compression ratio or turbocharge. Hence, we performed thermodynamic cycle analysis with changes in the intake-valve closing timing for the Otto–Miller cycle and evaluated the engine performance and Miller timing through the resulting problems and solutions. When only the compression ratio was compensated, the theoretical thermal efficiency of the Otto–Miller cycle improved by approximately 18.8% compared to that of the Otto cycle. In terms of thermal efficiency, it is more advantageous to compensate only the compression ratio; however, when considering the output of the engine, it is advantageous to also compensate the boost pressure to maintain the intake air mass flow rate.

Simulation of Extended Expansion Lean Burn Spark Ignition Engine

2004 ◽  
Author(s):  
A. Manivannan ◽  
R. Ramprabhu ◽  
P. Tamilporai ◽  
S. Chandrasekaran
Keyword(s):  
Heat Transfer ◽  
Compression Ratio ◽  
Thermal Efficiency ◽  
Numerical Study ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Valve Closure ◽  
Intake Valve ◽  
Lean Burn ◽  
Atkinson Cycle

This paper deals with Numerical Study of 4-stoke, Single cylinder, Spark Ignition, Extended Expansion Lean Burn Engine. Engine processes are simulated using thermodynamic and global modeling techniques. In the simulation study following process are considered compression, combustion, and expansion. Sub-models are used to include effect due to gas exchange process, heat transfer and friction. Wiebe heat release formula was used to predict the cylinder pressure, which was used to find out the indicated work done. The heat transfer from the cylinder, friction and pumping losses also were taken into account to predict the brake mean effective pressure, brake thermal efficiency and brake specific fuel consumption. Extended Expansion Engine operates on Otto-Atkinson cycle. Late Intake Valve Closure (LIVC) technique is used to control the load. The Atkinson cycle has lager expansion ratio than compression ratio. This is achieved by increasing the geometric compression ratio and employing LIVC. Simulation result shows that there is an increase in thermal efficiency up to a certain limit of intake valve closure timing. Optimum performance is attained at 90 deg intake valve closure (IVC) timing further delaying the intake valve closure reduces the engine performance.

Effect of Ethanol-Air Equivalence Ratio on Performance of an Endoreversible Otto Engine

2011 ◽  
Vol 110-116 ◽  
pp. 273-277
Author(s):  
Rahim Ebrahim ◽  
Mahmoud Reza Tadayon ◽  
Farshad Tahmasebi Gandomkari ◽  
Kamyar Mahbobian
Keyword(s):  
Performance Evaluation ◽  
Compression Ratio ◽  
Power Output ◽  
Thermal Efficiency ◽  
Equivalence Ratio ◽  
Maximum Power ◽  
Otto Cycle ◽  
World Community ◽  
Maximum Power Output ◽  
The World

Today, the world community is looking for fuel efficient and environmentally viable alternatives for many of the traditional energy conversion approaches. This development has further worked to increase the technical focus on conventional cycles for making them more optimum in terms of performance. Hence, the objective of this paper is to study the effect of ethanol-air equivalence ratio on the power output and the indicated thermal efficiency of an air standard Otto cycle. Optimization of the cycle has been performed for power output as well as for thermal efficiency with respect to compression ratio. The results show that the maximum power output, the optimal compression ratio corresponding to maximum power output point, the optimal compression ratio corresponding to maximum thermal efficiency point and the working range of the cycle first increase and then decrease as the equivalence ratio increases. The result obtained herein provides a guide to the performance evaluation and improvement for practical Otto engines.

scholarly journals EFFECT OF COMPRESSION RATIO ON PERFORMANCE OF A HYDROGEN BLENDED CNG-DIESEL DUAL FUEL ENGINE

2015 ◽  
Vol 44 (2) ◽  
pp. 87-93 ◽  
Author(s):  
Sridhara Reddy ◽  
Maheswar Dutta ◽  
K.Vijaya Kumar Reddy
Keyword(s):  
Energy Consumption ◽  
Specific Energy ◽  
Compression Ratio ◽  
Thermal Efficiency ◽  
Specific Energy Consumption ◽  
Dual Fuel ◽  
Operating Parameters ◽  
Brake Thermal Efficiency ◽  
Performance And Emission ◽  
Emission Behavior

Compression ratios of the engine considerably affect the performance and emission behavior of an engine.The paper discusses about effect of compression ratios on the operating parameters such as brake specific fuelconsumption (BSFC), brake specific energy consumption (BSEC), brake thermal efficiency (BTE) and volumetricefficiency on a stationary diesel-CNG dual fuel engine by adding hydrogen fraction as a combustion booster. Theexhaust emission behavior of the engine is also presented. Addition of hydrogen in CNG has given better resultsthan diesel-CNG dual fuel operation of the engine. The volumetric efficiency and emissions like NOx are theparameters which needed attention towards this study. The paper presents experimental results and analyzes them.

Application of Over-Expansion Cycle to a Larger Gasoline Engine With Late-Closing of Intake Valves

2002 ◽  
Author(s):  
Seiichi Shiga ◽  
Kenji Nishida ◽  
Shizuo Yagi ◽  
Youichi Miyashita ◽  
Yoshiharu Yuzawa ◽  
...  
Keyword(s):  
Compression Ratio ◽  
Thermal Efficiency ◽  
Gasoline Engine ◽  
Engine Performance ◽  
Mechanical Efficiency ◽  
Expansion Ratio ◽  
Brake Thermal Efficiency ◽  
Gasoline Engines ◽  
Cylinder Test ◽  
Test Engine

This paper presents further investigation into the effect of over-expansion cycle with late-closing of intake valves on the engine performance in gasoline engines. A larger single-cylinder test engine with the stroke volume of 650 cc was used with four kinds of expansion ratio (geometrical compression ratio) from 10 to 25 and four sets of intake valve closure (I.V.C.) timings from 0 to 110 deg C.A. ABDC. Late-closing has an effect of decreasing the pumping work due to the reduction of intake vacuum, althogh higher expansion ratio increases the friction work due to the average cylinder pressure level. Combining the higher expansion ratio with the late-closing determines the mechanical efficiency on the basis of these two contrastive effects. The indicated thermal efficiency is mostly determined by the expansion ratio and little affected by the nominal compression ratio. The value of the indicated thermal efficiency reaches to 48% at most which is almost comparable with the value of diesel engines. The improvement of both indicated and brake thermal efficiency reaches to 16% which is much higher than ever reported by the authors. A simple thermodynamic calculation could successfully explain the behavior of the indicated thermal efficiency. The brake thermal efficiency could also be improved due to the increase in both mechanical and indicated efficiencies.

THE OXIDATION, IGNITION, AND DETONATION OF FUEL VAPORS AND GASES: XII. THE HIGH COMPRESSION RATIO OTTO CYCLE GAS ENGINE AND THE ADVERSE EFFECT OF HIGH JACKET TEMPERATURES ON THERMAL EFFICIENCY

1949 ◽  
Vol 27f (11) ◽  
pp. 435-449 ◽  
Author(s):  
R. O. King ◽  
Edwin J. Durand ◽  
J. Alex. Morrison
Keyword(s):  
Adverse Effect ◽  
Quality Control ◽  
Compression Ratio ◽  
Thermal Efficiency ◽  
Diesel Oil ◽  
Surface Combustion ◽  
Compression Ignition ◽  
Otto Cycle ◽  
High Compression Ratio ◽  
Gas Engine

Town gas was used as the fuel for the C.F.R. engine during a series of engine trials run at a compression ratio of 10:1 and at jacket temperatures of 140°, 212°, 302°, and 351° F. The mixture strength at each jacket temperature was varied from the weakest to the richest on which the engine would run steadily. The object of the trials was (1) to determine the effect of jacket temperature on thermal efficiency and (2) to compare the performance of an Otto cycle engine run at 10:1 compression ratio with that of a compression ignition (Diesel) oil engine. The results of the trials show that thermal efficiency decreases as the jacket temperature is raised, that is, the decrease more than offsets the gain due to decrease of heat loss during combustion and expansion. It is indicated by the character of the results and by experiments described earlier that the observed loss of efficiency is due to flameless surface combustion of the fuel during compression. The performance of the C.F.R. engine running on town gas at 10:1 compression ratio as compared with that of a compression ignition oil engine running at 12:1 was superior in respect of maximum power (I.M.E.P.) developed and range of quality control and not greatly inferior in respect of thermal efficiency.

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