Quantification of Efficiency Gains for Dilute IC Engines due to Increases of the Ratio of Specific Heats

2014 ◽  
Author(s):  
Jerald A. Caton
Keyword(s):  
Thermal Efficiency ◽  
Heat Losses ◽  
Efficiency Gains ◽  
Automotive Engine ◽  
Specific Heats ◽  
Cycle Simulation ◽  
Lack Of Information ◽  
Ic Engines ◽  
Lean Mixtures ◽  
Gas Recirculation

Recent engine developments have demonstrated significant thermal efficiency gains for IC engines employing lean mixtures and high levels of exhaust gas recirculation (EGR). These efficiency gains have often been attributed to reduced heat losses and increases of the ratio of specific heats. No previous publication, however, has provided the quantitative contributions from these two items. This lack of information, therefore, motivated the current work. An automotive engine was selected for this study, and a thermodynamic engine cycle simulation was used for the evaluation. Engine conditions included a range of loads and speeds. For each engine condition, three cases were considered. These cases varied the equivalence ratio from stoichiometric to 0.7, and varied the EGR from zero to 45%. Depending on the engine conditions, the net indicated thermal efficiency increased between 4.2% and 8.9% (absolute) for the engine with the lean mixture (ϕ = 0.7) and EGR (45%). The lower gas temperatures and lean mixtures resulted in reduced heat losses and increases of the ratio of specific heats. For all conditions examined, the majority of the thermal efficiency gains were due to the increases of the ratio of specific heats. The contributions from the increases of the ratio of specific heats toward the efficiency gains ranged between about 46% and 82% for the conditions examined. The rest of the gains were from the reduced heat losses.

Maximum efficiencies for internal combustion engines: Thermodynamic limitations

2017 ◽  
Vol 19 (10) ◽  
pp. 1005-1023 ◽  
Author(s):  
Jerald A Caton
Keyword(s):  
Heat Transfer ◽  
Internal Combustion Engines ◽  
High Efficiency ◽  
Pressure Rise ◽  
Internal Combustion ◽  
Thermodynamic Evaluation ◽  
Combustion Engines ◽  
Automotive Engine ◽  
Specific Heats ◽  
Cycle Simulation

The thermodynamic limitation for the maximum efficiencies of internal combustion engines is an important consideration for the design and development of future engines. Knowing these limits helps direct resources to those areas with the most potential for improvements. Using an engine cycle simulation which includes the first and second laws of thermodynamics, this study has determined the fundamental thermodynamics that are responsible for these limits. This work has considered an automotive engine and has quantified the maximum efficiencies starting with the most ideal conditions. These ideal conditions included no heat losses, no mechanical friction, lean operation, and short burn durations. Then, each of these idealizations is removed in a step-by-step fashion until a configuration that represents current engines is obtained. During this process, a systematic thermodynamic evaluation was completed to determine the fundamental reasons for the limitations of the maximum efficiencies. For the most ideal assumptions, for compression ratios of 20 and 30, the thermal efficiencies were 62.5% and 66.9%, respectively. These limits are largely a result of the combustion irreversibilities. As each of the idealizations is relaxed, the thermal efficiencies continue to decrease. High compression ratios are identified as an important aspect for high-efficiency engines. Cylinder heat transfer was found to be one of the largest impediments to high efficiency. Reducing cylinder heat transfer, however, is difficult and may not result in much direct increases of piston work due to decreases of the ratio of specific heats. Throughout this work, the importance of high values of the ratio of specific heats was identified as important for achieving high thermal efficiencies. Depending on the selection of constraints, different values may be given for the maximum thermal efficiency. These constraints include the allowed values for compression ratio, heat transfer, friction, stoichiometry, cylinder pressure, and pressure rise rate.

Thermodynamic Considerations for Advanced, High Efficiency IC Engines

2013 ◽  
Author(s):  
Jerald A. Caton
Keyword(s):  
High Efficiency ◽  
Heat Losses ◽  
Not Given ◽  
Engine Operation ◽  
Brake Thermal Efficiency ◽  
Detailed Understanding ◽  
Specific Heats ◽  
Combustion Duration ◽  
Ic Engines ◽  
Full Consideration

Thermodynamics is the key discipline for determining and quantifying the elements of advanced engine designs which lead to high efficiency. In spite of its importance, thermodynamics is often not given full consideration in understanding engine operation for high efficiency. By fully utilizing the first and second laws of thermodynamics, detailed understanding of the engine features that provide for high efficiency may be determined. Of all the possible features that contribute to high efficiency, the results of this study show that highly diluted engines with high compression ratios provide the greatest impact for high efficiencies. Other important improvements which increase the efficiency include reduced heat losses, optimal combustion phasing, reduced friction, and reduced combustion duration. Thermodynamic quantification of these concepts is provided. For one comparison, the brake thermal efficiency increased from about 34% for the conventional engine to about 48% for the engine with one set of the above features. One aspect that contributes to these improvements is the importance of the ratio of specific heats (“gamma”). In addition, these design features often result in low emissions due to the low combustion temperatures.

Thermodynamic Considerations for Advanced, High Efficiency IC Engines

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Jerald A. Caton
Keyword(s):  
High Efficiency ◽  
Heat Losses ◽  
Not Given ◽  
Engine Operation ◽  
Brake Thermal Efficiency ◽  
Detailed Understanding ◽  
Specific Heats ◽  
Combustion Duration ◽  
Ic Engines ◽  
Full Consideration

Thermodynamics is the key discipline for determining and quantifying the elements of advanced engine designs, which lead to high efficiency. In spite of its importance, thermodynamics is often not given full consideration in understanding engine operation for high efficiency. By fully utilizing the first and second laws of thermodynamics, detailed understanding of the engine features that provide for high efficiency may be determined. Of all the possible features that contribute to high efficiency, the results of this study show that highly diluted engines with high compression ratios provide the greatest impact for high efficiencies. Other important improvements, which increase the efficiency include reduced heat losses, optimal combustion phasing, reduced friction, and reduced combustion duration. Thermodynamic quantification of these concepts is provided. For one comparison, the brake thermal efficiency increased from about 34% for the conventional engine to about 48% for the engine with one set of the above features. One aspect that contributes to these improvements is the importance of the increase of the ratio of specific heats. In addition, these design features often result in low emissions due to the low combustion temperatures.

scholarly journals Thermal Efficiency Gains Enabled by Using CO2 Mixtures in Supercritical Power Cycles

Energy ◽  
2021 ◽  
pp. 121899
Author(s):  
F. Crespi ◽  
P. Rodríguez de Arriba ◽  
D. Sánchez ◽  
A. Ayub ◽  
G. Di Marcoberardino ◽  
...  
Keyword(s):  
Thermal Efficiency ◽  
Efficiency Gains ◽  
Power Cycles

scholarly journals Impact of injection strategies on combustion characteristics, efficiency and emissions of gasoline compression ignition operation in a heavy-duty multi-cylinder engine

2018 ◽  
Vol 21 (8) ◽  
pp. 1426-1440 ◽  
Author(s):  
Buyu Wang ◽  
Michael Pamminger ◽  
Ryan Vojtech ◽  
Thomas Wallner
Keyword(s):  
High Temperature ◽  
Thermal Efficiency ◽  
Fuel Injection ◽  
Pressure Rise ◽  
Pilot Injection ◽  
Low Temperature Combustion ◽  
Compression Ignition ◽  
Temperature Combustion ◽  
Gas Recirculation ◽  
Direct Fuel Injection

Gasoline compression ignition using a single gasoline-type fuel for direct/port injection has been shown as a method to achieve low-temperature combustion with low engine-out NOx and soot emissions and high indicated thermal efficiency. However, key technical barriers to achieving low-temperature combustion on multi-cylinder engines include the air handling system (limited amount of exhaust gas recirculation) as well as mechanical engine limitations (e.g. peak pressure rise rate). In light of these limitations, high-temperature combustion with reduced amounts of exhaust gas recirculation appears more practical. Furthermore, for high-temperature gasoline compression ignition, an effective aftertreatment system allows high thermal efficiency with low tailpipe-out emissions. In this work, experimental testing was conducted on a 12.4 L multi-cylinder heavy-duty diesel engine operating with high-temperature gasoline compression ignition combustion with port and direct injection. Engine testing was conducted at an engine speed of 1038 r/min and brake mean effective pressure of 1.4 MPa for three injection strategies, late pilot injection, early pilot injection, and port/direct fuel injection. The impact on engine performance and emissions with respect to varying the combustion phasing were quantified within this study. At the same combustion phasing, early pilot injection and port/direct fuel injection had an earlier start of combustion and higher maximum pressure rise rates than late pilot injection attributable to more premixed fuel from pilot or port injection; however, brake thermal efficiencies were higher with late pilot injection due to reduced heat transfer. Early pilot injection also exhibited the highest cylinder-to-cylinder variations due to differences in injector behavior as well as the spray/wall interactions affecting mixing and evaporation process. Overall, peak brake thermal efficiency of 46.1% and 46% for late pilot injection and port/direct fuel injection was achieved comparable to diesel baseline (45.9%), while early pilot injection showed the lowest brake thermal efficiency (45.3%).

Mukhaizna Steam Injectors Thermal Efficiency & Insulated tubing Pilot Evaluation

2015 ◽  
Author(s):  
Rashid Al Shaibi
Keyword(s):  
Thermal Efficiency ◽  
Outer Wall ◽  
Heat Losses ◽  
Oil Field ◽  
Evaluation Methodology ◽  
Base Line ◽  
Field Observations ◽  
Reference Base ◽  
Steam Flood ◽  
Deep Reservoir

Abstract Occidental operates a steam flood project in Mukhaizna which is a giant deep heavy oil field in south Oman. Wellbore heat losses from steam injectors is one of the challenges that degrades the steam flood thermal efficiency for a deep reservoir. In addition, wellbore heat losses increase the thermal stress on the casing and lead to wellbore damage. In aim to reduce wellbore heat losses, insulated tubing was introduced and a Pilot was carried out to select the optimum insulated tubing product in the market. Ten Injectors were instrumented and completed with insulated tubing from four different vendors in addition to two bare strings used as a reference base line. Data were collected and evaluated in eight months period. Field thermal conductivity was obtained for the tested products using DTS temperature data from the outermost casing, the Thermocouples data from the tubing outer wall and temperature logs during injection in aid of a calibrated wellbore model. The conducted analysis and the field observations were sufficient to resolve the thermal performance between the tested products. This paper describes the Pilot configuration and the evaluation methodology. Analysis output and field observations are summarized and presented in addition to the raw data collected from the instruments and temperature logs.

The impact of water injection and exhaust gas recirculation on combustion and emissions in a heavy-duty compression ignition engine operated on diesel and gasoline

2019 ◽  
Vol 21 (8) ◽  
pp. 1555-1573 ◽  
Author(s):  
Michael Pamminger ◽  
Buyu Wang ◽  
Carrie M Hall ◽  
Ryan Vojtech ◽  
Thomas Wallner
Keyword(s):  
Thermal Efficiency ◽  
Water Injection ◽  
Combustion Process ◽  
Exhaust Gas Recirculation ◽  
Exhaust Gas ◽  
Brake Thermal Efficiency ◽  
Fuel Ratio ◽  
Main Injection ◽  
Gas Recirculation ◽  
Diesel Operation

Steady-state experiments were conducted on a 12.4L, six-cylinder heavy-duty engine to investigate the influence of port-injected water and dilution via exhaust gas recirculation (EGR) on combustion and emissions for diesel and gasoline operation. Adding a diluent to the combustion process reduces peak combustion temperatures and can reduce the reactivity of the charge, thereby increasing the ignition-delay and, allowing for more time to premix air and fuel. Experiments spanned water/fuel mass ratios up to 140mass% and exhaust gas recirculation ratios up to 20vol% for gasoline and diesel operation with different injection strategies. Diluting the combustion process with either water or EGR resulted in a significant reduction in nitrogen oxide emissions along with a reduction in brake thermal efficiency. The sensitivity of brake thermal efficiency to water and EGR varied among the fuels and injection strategies investigated. An efficiency breakdown revealed that water injection considerably reduced the wall heat transfer; however, a substantial increase in exhaust enthalpy offset the reduction in wall heat transfer and led to a reduction in brake thermal efficiency. Regular diesel operation with main and post injection exhibited a brake thermal efficiency of 45.8% and a 0.3% reduction at a water/fuel ratio of 120%. The engine operation with gasoline, early pilot, and main injection strategy showed a brake thermal efficiency of 45.0% at 0% water/fuel ratio, and a 1.2% decrease in brake thermal efficiency for a water/fuel ratio of 140%. Using EGR as a diluent reduced the brake thermal efficiency by 0.3% for diesel operation, comparing ratios of 0% and 20% EGR. However, a higher impact on brake thermal efficiency was seen for gasoline operation with early pilot and main injection strategy, with a reduction of about 0.8% comparing 0% and 20% EGR. Dilution by means of EGR exhibited a reduction in nitrogen oxide emissions up to 15 g/kWh; water injection showed only up to 10 g/kWh reduction for the EGR rates and water/fuel ratio investigated.

Development of an exhaust gas recirculation strategy for an acetylene-fuelled homogeneous charge compression ignition engine

2010 ◽  
Vol 224 (7) ◽  
pp. 941-952 ◽  
Author(s):  
K Sudheesh ◽  
J M Mallikarjuna
Keyword(s):  
Thermal Efficiency ◽  
Homogeneous Charge Compression Ignition ◽  
Exhaust Gas Recirculation ◽  
Electrical Heating ◽  
Exhaust Gas ◽  
Compression Ignition ◽  
Brake Thermal Efficiency ◽  
Load Limit ◽  
Gas Recirculation ◽  
Load Conditions

This paper deals with experimental investigations carried out to develop an exhaust gas recirculation (EGR) strategy for an acetylene-fuelled homogeneous charge compression ignition (HCCI) engine. This study involves an analysis of the external inlet charge heating, the use of a mix of hot EGR and cool EGR to extend the load range, and the performance of the engine in the acetylene HCCI mode. First, experiments are conducted on a single-cylinder engine in the acetylene HCCI mode with external electrical heating at different load conditions, and the best inlet charge temperatures at each load condition are obtained. Second, hot EGR or a mix of hot EGR and cool EGR (i.e. the EGR strategy) is used to reduce or eliminate external charge heating and to extend the upper load limit, or to improve the brake thermal efficiency. In both cases, the engine performance is compared with that of the conventional diesel compression ignition (CI) mode. It is found that with EGR, above 25 per cent of load, the upper load limit at different inlet charge temperatures increases by about 16 28 per cent without any external charge heating. Below 25 per cent of load, the electrical heating at different inlet charge conditions is reduced by about 67–87 per cent. The brake thermal efficiency increases by 5–24 per cent under all the load conditions and it is comparable with that in the conventional CI mode. In the HCCI mode, nitrogen oxide levels are less than 20ppm. Smoke levels are always lower than 0.1 Bosch smoke unit. Hydrocarbon and carbon monoxide emissions are relatively higher than for the conventional CI mode.

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