The Effects of Compression Ratio and Expansion Ratio on Engine Performance Including the Second Law of Thermodynamics: Results From a Cycle Simulation

2007 ◽  
Author(s):  
Jerald A. Caton
Keyword(s):  
Compression Ratio ◽  
Engine Performance ◽  
Expansion Ratio ◽  
Heat Losses ◽  
Spark Ignition Engine ◽  
Maximum Efficiency ◽  
Second Law ◽  
Part Load ◽  
Cycle Simulation ◽  
Large Expansion

This investigation quantified the effects of compression ratio and expansion ratio on performance, efficiency, and second law parameters for an automotive, spark-ignition engine. The well known increase in engine performance for increasing compression ratio and expansion ratio is demonstrated. These increases for brake engine performance are modest for compression ratios greater than about 10 for the conditions studied. The results demonstrated that the increasing friction and heat losses for the higher compression ratios are of the same order as the thermodynamic gains. Also, the results included the destruction of availability during combustion. For a part load condition, the availability destroyed decreased from about 23% for a compression ratio of 4 to about 21% for a compression ratio of 10. In addition, this study examined cases with greater expansion ratios than compression ratios. The overall cycle for these cases is often called an “Atkinson” cycle. For most cases, the thermal efficiency first increased as expansion ratio increased, attained a maximum efficiency, and then decreased. The decrease in efficiency after the maximum value was due to increased heat losses, increased friction, and ineffective exhaust processes (due to the reduced cylinder pressure at the time of exhaust valve opening). For part load cases, the higher expansion ratio provided only modest gains due to increased pumping losses associated with the constant load requirement. For the wide open throttle cases, however, the higher expansion ratios provided significant gains. For example, for a compression ratio of 10, expansion ratios of 10 and 30 provided brake thermal efficiencies of about 34% and 43%, respectively. Although the net thermodynamic gains are significant, large expansion ratios such as 30 may not be practical in most applications.

Results From an Engine Cycle Simulation of Compression Ratio and Expansion Ratio Effects on Engine Performance

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Jerald A. Caton
Keyword(s):  
Compression Ratio ◽  
Load Condition ◽  
Engine Performance ◽  
Constant Load ◽  
Expansion Ratio ◽  
Heat Losses ◽  
Spark Ignition Engine ◽  
Maximum Efficiency ◽  
Part Load ◽  
Cycle Simulation

This investigation quantified the effects of compression ratio (CR) and expansion ratio (ER) on performance, efficiency, and second law parameters for an automotive, spark-ignition engine. The well known increase in engine performance for increasing CR and ER is demonstrated. These increases for brake engine performance are modest for CRs greater than about 10 for the conditions studied. The results demonstrated that the increasing friction and heat losses for the higher CRs are of the same order as the thermodynamic gains. Also, the results included the destruction of availability during combustion. For a part load condition, the availability destroyed decreased from about 23% to 21% for CRs of 4 and 10, respectively. In addition, this study examined cases with greater ERs than CRs. The overall cycle for these cases is often called an “Atkinson” cycle. For most cases, the thermal efficiency first increased as ER increased, attained a maximum efficiency, and then decreased. The decrease in efficiency after the maximum value was due to the increased heat losses, increased friction, and ineffective exhaust processes (due to the reduced cylinder pressure at the time of exhaust valve opening). For part load cases, the higher ER provided only modest gains due to the increased pumping losses associated with the constant load requirement. For the wide open throttle cases, however, the higher ERs provided significant gains. For example, for a compression ratio of 10, expansion ratios of 10 and 30 provided brake thermal efficiencies of about 34% and 43%, respectively. Although the net thermodynamic gains are significant, large ERs such as 30 may not be practical in most applications.

A Multiple-Zone Cycle Simulation for Spark-Ignition Engines: Thermodynamic Details

2001 ◽  
Author(s):  
Jerald A. Caton
Keyword(s):  
Combustion Process ◽  
Load Condition ◽  
Engine Performance ◽  
Thermodynamic Cycle ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Engine Operation ◽  
Part Load ◽  
Cycle Simulation ◽  
The Individual

Abstract A thermodynamic cycle simulation was developed for a spark-ignition engine which included the use of multiple zones for the combustion process. This simulation was used to complete analyses for a commercial, spark-ignition V-8 engine operating at a part load condition. Specifically, the engine possessed a compression ratio of 8.1:1, and had a bore and stroke of 101.6 and 88.4 mm, respectively. A part load operating condition at 1400 rpm with an equivalence ratio of 1.0 was examined. Results were obtained for overall engine performance, for detailed in-cylinder events, and for the thermodynamics of the individual processes. In particular, the characteristics of the engine operation with respect to the combustion process were examined. Implications of the multiple zones formulation for the combustion process are described.

A Turbocharged, Spark-Ignition Engine: Results From an Engine Cycle Simulation Including the Second Law of Thermodynamics

2009 ◽  
Author(s):  
Vaibhav J. Lawand ◽  
Jerald A. Caton
Keyword(s):  
Combustion Process ◽  
Engine Performance ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Spark Ignition Engine ◽  
Second Law ◽  
Base Case ◽  
Mixing Processes ◽  
Automotive Engine ◽  
Cycle Simulation

The use of turbocharging systems for spark-ignition engines has seen increased interest in recent years due to the importance of fuel efficiency, and in some cases, increased performance. An example of a possible strategy is to use a smaller displacement engine with turbocharging rather than a larger engine without turbocharging. To better understand the tradeoffs and the fundamental aspects of a turbocharged engine, this investigation is aimed at determining the energy and exergy quantities for a range of operating conditions for a spark-ignition engine. A 3.8 liter automotive engine with a turbocharger and intercooler was selected for this study. Various engine performance and other output parameters were determined as functions of engine speed and load. For the base case (2000 rpm and a bmep of 1200 kPa), the bsfc was about 240 g/kW-h. At these conditions, the second law analysis indicated that the original fuel exergy was distributed as follows: 34.7% was delivered as indicated work, 16.9% was moved via heat transfer to the cylinder walls, 23.0% exited with the exhaust gases, 20.6% was destroyed during the combustion process, 2.5% was destroyed due to inlet mixing processes, and 1.9% was destroyed due to the exhaust processes. The turbocharger components including the intercooler were responsible for less than 1.0% of the fuel exergy destruction or transfer.

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.

A Theoretical Study of a Variable Compression Ratio Turbocharged Diesel Engine

1992 ◽  
Vol 206 (4) ◽  
pp. 227-238 ◽  
Author(s):  
T J Rychter ◽  
A Teodorczyk ◽  
C R Stone ◽  
H J Leonard ◽  
N Ladommatos ◽  
...  
Keyword(s):  
Diesel Engine ◽  
Compression Ratio ◽  
Engine Performance ◽  
Expansion Ratio ◽  
Combustion Noise ◽  
Connecting Rod ◽  
Turbocharged Diesel Engine ◽  
Variable Compression Ratio ◽  
Engine Simulation ◽  
Variable Compression

A variable compression ratio concept that can give a different expansion ratio to the compression ratio has been evaluated by means of a simulation of a turbocharged diesel engine. The compression ratio is controlled by varying the ratio of the connecting rod length to the crank throw, hence the name variable crank radius/connecting rod length engine (VR/LE). The VR/LE mechanism kinematics have been defined and described, and the compression ratio and expansion ratio have been presented as a function of the eccentric phase angle (αo). A zero-dimensional engine simulation that has been the subject of comprehensive validation has been used as the basis of the VR/LE study. The effect of the compression ratio on the engine performance at fixed loads is presented. The principal benefits are a reduction in fuel consumption at part load of about 2 per cent and a reduction in ignition delay that leads to an estimated 6 dB reduction in combustion noise. The study has been conducted within the assumption of a maximum cylinder pressure of 160 bar.

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.

First and Second Law Analyses of a Spark-Ignition Engine Using Either Isooctane or Hydrogen: An Initial Assessment

2006 ◽  
Author(s):  
Jerald A. Caton
Keyword(s):  
Nitric Oxide ◽  
Thermal Efficiency ◽  
Equivalence Ratio ◽  
Performance Metrics ◽  
Combustion Process ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Second Law ◽  
Cycle Simulation ◽  
Nitric Oxide Emissions

The use of either hydrogen or isooctane for a spark-ignition engine was examined using a thermodynamic cycle simulation including the second law of thermodynamics. The engine studied was a 5.7 liter, automotive engine operating from idle to wide open throttle. The hydrogen or isooctane was assumed premixed with the air. Two features of hydrogen combustion that were included in the study were the higher flame speeds (shorter burn durations) and the wider lean flammability limits (lean equivalence ratios). Three cases were considered for the use of hydrogen: (1) standard burn duration and an equivalence ratio of 1.0, (2) a shorter burn duration and an equivalence ratio of 1.0, and (3) a shorter burn duration and variable, lean equivalence ratios. The results included thermal efficiencies, other performance metrics, second law parameters, and nitric oxide emissions. In general, for the cases with an equivalence of 1.0, the brake thermal efficiency was slightly lower for the hydrogen cases due to the higher temperatures and higher heat losses. For the variable, lean equivalence ratio cases, the thermal efficiency was higher for the hydrogen case relative to the isooctane case. Due to the higher temperatures, the hydrogen cases had over 50% higher nitric oxide emissions compared to the isooctane case at the base conditions. In addition, the second law analyses indicated that the destruction of availability during the combustion process was lower for the base hydrogen case (11.2%) relative to the isooctane case (21.1%).

scholarly journals Influence of Compression Ratio on Flywheel Dimension for a Naturally Aspirated Spark Ignition Engine: A Numerical Study

2020 ◽  
Vol 3 (2) ◽  
Author(s):  
Aan Yudianto ◽  
Peixuan Li
Keyword(s):  
Compression Ratio ◽  
Numerical Study ◽  
Engine Performance ◽  
Spark Ignition ◽  
Spark Ignition Engine ◽  
Effective Pressure ◽  
Si Engine ◽  
Compression Stroke ◽  
Indicated Mean Effective Pressure ◽  
Proper Design

The proper design of the flywheel undeniably determines in tuning the engine to confirm the better output engine performance. The aim of this study is to mathematically investigate the effect of various values of the compression ratio on some essential parameters to determine the appropriate value for the flywheel dimension. A numerical calculation approach was proposed to eventually determine the dimension of the engine flywheel on a five-cylinder four-stroke Spark Ignition (SI) engine. The various compression ratios of 8.5, 9, 9.5, 10, 10.5, and 11 were selected to perform the calculations. The effects of compression ratio on effective pressure, indicated mean effective pressure (IMEP), dynamic irregularity value of the crankshaft, and the diameter of the flywheel was clearly investigated. The study found that 2.5 increment value of the compression ratio significantly increases the effective pressure of about 41.53% on the starting of the expansion stroke. While at the end of the compression stroke, the rise of effective pressure is about 76.67%, and the changes in dynamic irregularity merely increase by about 1.79%. The same trend applies to the flywheel diameter and width, which increases 2.08% for both.

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