Thermodynamic modeling of spark-ignition engine: Effect of temperature dependent specific heats

This paper presents thermodynamics analysis of spark-ignition (SI) engine. A theoretical model of air-standard Otto cycle having temperature dependent specific heats has been implemented. It was compared to that which uses constant temperature specific heats. Wide range of engine parameters was studied. In most cases there were significant variations between the results obtained by using temperature dependent specific heats with those obtained at constant specific heats especially at high engine speeds. Therefore, it is more realistic to use temperature dependent specific heat. This should be considered in cycle analysis; especially that temperature variation in the actual cycles is quite large.     

Comparison of performance of compact chamber spark‐ignition engine with conventional S.I. engine

This paper deals with the compact chamber engine in which a bowl‐like space in the piston or head of the cylinder is added to cause swirling of the air–fuel mixture. This causes a change in performance from the conventional spark ignition engine. In this work, the operating variables considered are the engine speed, equivalence ratio, inlet pressure and temperature and exhaust pressure. A computer program is specially devised to calculate performance at design and off design operation conditions. The compact chamber achieves an increase in volumetric efficiency of 5%. The brake efficiency is 28.5%, whereas for conventional SI engine is 23%, with an increase of 20%. The brake power for the compact chamber engine is 39 kW, whereas for the conventional engine is 35 kW, an increase of 10%. Hence, the reduction in the brake‐specific fuel consumption is about 20%. Copyright © 2010 John Wiley & Sons, Ltd.     

A comparison between EGR and lean-burn strategies employed in a natural gas SI engine using a two-zone combustion model

Exhaust gas recirculation (EGR) strategy has been recently employed in natural gas SI engines as an alternative to lean burn technique in order to satisfy the increasingly stringent emission standards. However, the effect of EGR on some of engine performance parameters compared to lean burn is not yet quite certain. In the current study, the effect of both EGR and lean burn on natural gas SI engine performance was compared at similar operating conditions. This was achieved numerically by developing a computer simulation of the four-stroke spark-ignition natural gas engine. A two-zone combustion model was developed to simulate the in-cylinder conditions during combustion. A kinetic model based on the extended Zeldovich mechanism was also developed in order to predict NO emission. The combustion model was validated using experimental data and a good agreement between the results was found. It was demonstrated that adding EGR to the stoichiometric inlet charge at constant inlet pressure of 130 kPa decreased power more rapidly than excess air; however, the power loss was recovered by increasing the inlet pressure from 130 kPa at zero dilution to 150 kPa at 20% EGR dilution. The engine fuel consumption increased by 10% when 20% EGR dilution was added at inlet pressure of 150 kPa compared to using 20% air dilution at 130 kPa. However, it was found that EGR dilution strategy is capable of producing extremely lower NO emission than lean burn technique. NO emission was reduced by about 70% when the inlet charge was diluted at a rate of 20% using EGR instead of excess air.     

Availability analysis of a coke oven gas fueled spark ignition engine

The current work investigates a coke oven gas fueled spark ignition (SI) engine from the perspective of the first and second laws in order to understand the energy conversion performance of fuels and achieve highly efficient utilization. A detailed energy and exergy analysis is applied to a quasi-dimensional two-zone spark ignition engine model which combines turbulence flame propagation speed model at 1500 rpm by changing gas fuel types, compression ratio, load and ignition timing. It was found that the irreversibility of methane is the maximum and that of syngas is the minimum among the three different fuels. The irreversibility in the combustion process of a coke oven gas fueled SI engine is reduced when the compression ratio or the throttle valve opening angle is increased and the ignition timing is delayed. Increasing the compression ratio and delaying the ignition timing can improve the first and second law efficiency and reduce the brake specific fuel consumption (BSFC). The power performance and fuel economy are good and the energy is also used effectively when the compression ratio is 11, the throttle angle is 90% and the ignition time is ?10° CA ATDC respectively.     

The effect of reformer gas mixture on the performance and emissions of an HSDI diesel engine

Exhaust gas assisted fuel reforming is an attractive on-board hydrogen production method, which can open new frontiers in diesel engines. Apart from hydrogen, and depending on the reactions promoted, the reformate typically contains a significant amount of carbon monoxide, which is produced as a by-product. Moreover, admission of reformed gas into the engine, through the inlet pipe, leads to an increase of intake air nitrogen to oxygen ratio. It is therefore necessary to study how a mixture of syngas and nitrogen affects the performance and emissions of a diesel engine, in order to gain a better understanding of the effects of supplying fuel reformer products into the engine.     

Performance of a micro engine with heptane as working fluid

A micro Newcomen engine is proposed. To overcome the problems of friction and leakage of the micro mechanical parts during engine’s operation, we use a flexible ripple tube to integrate piston and cylinder into one monolithic part. Heptane is used as the working fluid, and it works in the two-phase condition for higher energy output density per thermodynamic cycle. In the experiment, the prototype engine is tested under different operational conditions. It works continuously and generates the net mechanical work of 0.833 J per cycle with an efficiency of 2.77% in the maximum. The experimental results prove its feasibility. However, the prototype engine still requires further improvement and optimization for better performance.     

Effects of ignition advance on a dual sequential ignition engine at lean mixture for hydrogen enriched butane usage

In this study, the effects of ignition advance on dual sequential ignition engine characteristics and exhaust gas emissions for hydrogen enriched butane usage and lean mixture were investigated numerically and experimentally. The main purpose of this study is to reveal the effects of h-butane application in a commercial spark ignition gasoline engine. One cylinder of the commercially dual sequential spark ignition engine was modeled in the Star-CD software, taking into account all the components of the combustion chamber (intake-exhaust manifold connections, intake-exhaust valves, cylinder, cylinder head, piston, spark plugs). Angelberger wall approximation, k-ε RNG turbulence model and G-equation combustion model were used for analysis. In the dual sequential spark ignition, the difference between the spark plugs was defined as 5° CAD. At the numerical analysis; 10.8:1 compression ratio, 1.3 air-fuel ratio, 2800 rpm engine speed, 0.0010 m the flame radius and 0.0001 m the flame thickness were kept constant. The hydrogen-butane mixture was defined as 4%–96% by mass. In the analysis, the optimal ignition advance was determined by the working conditions. In addition, the effects of changes in ignition advance were examined in detail at lean mixture. For engine operating conditions under investigation, it has been determined that the 50° CAD ignition advance from the top dead center is the optimal ignition advance in terms of engine performance and emission balance. It has also been found that the NO_x formation rises up as the ignition advance increases. The BTE values were approximately 12.01% higher than butane experimental results. The experimental BTE values for h-butane were overall 3.01% lower than h-butane numerical results.     

Thermodynamic analysis of sorption‐enhanced water–gas shift reaction using syngases

Sorption‐enhanced water–gas shift (SEWGS) reaction performance using syngas as the feedstock is investigated in this study based on thermodynamic equilibrium analysis. It was found that the capability of CO₂ sorbent in CO₂ removal was independent of the dry syngas composition. Regardless of the dry gas composition, CO₂ sorbent loses its adsorption capability as the reaction temperature increases higher than a temperature limit. This CO₂ adsorption temperature limit was found to depend on the steam to carbon (SC) ratio and reaction pressure. With the decrease in SC and increase in pressure the CO₂ adsorption temperature limit can be raised to a higher value. However, the initial CO₂ content in the syngas composition affects the carbon and CH₄ formations in SEWGS. For syngas with low CO₂ concentration, carbon formation can be completely eliminated and CH₄ formation can be reduced by CO₂ removal. For syngas with high CO₂ concentration, no carbon and CH₄ suppression can be found. It was also found that the temperature at which no carbon and CH₄ formations was increased to a higher value as the initial CO₂ concentration was increased. Copyright © 2016 John Wiley & Sons, Ltd.     

Combustion analysis of a spark ignition engine fueled with gaseous blends containing hydrogen

This paper presents the combustion characteristics of a naturally aspirated spark ignition engine, intended for installation in vehicles, fueled with different hydrogen and methane blends. The experimental tests were carried out in a wide range of speeds at equivalence ratios of 1, 0.8 and 0.7 and at full load. The ignition timing was maintained for each speed, independently of the equivalence ratio and blend used as fuel. Four methane-hydrogen blends were used. In-cylinder pressure, mass fraction burned, heat released and cycle-by-cycle variations were analyzed as representative indicators of the combustion quality. It was observed that hydrogen enrichment of the blend improve combustion for the ignition timing chosen. This improvement is more appreciable at low speeds, because at high speeds hydrogen effect is attenuated by the high turbulence. Also, hydrogen addition allowed the extension of the LOL, enabling the engine to run stable in points where methane could not be tested. The main inconvenience detected was the high NO_x emissions measured, especially at stoichiometric conditions, due mainly to the increment in the combustion temperature that hydrogen produces.     

Exergy destruction during the combustion process as functions of operating and design parameters for a spark‐ignition engine

The second law of thermodynamics provides different perspectives compared with the first law, and provides the property exergy. Exergy is a measure of the work potential of energy from a given thermodynamic state. Unlike energy, exergy may be destroyed, and for reciprocating engines, the major source of this destruction is during the combustion process. This paper provides an overview of the quantitative levels of exergy destruction during the combustion process as function of engine operating and design parameters, and for eight fuels. The results of this study are based on a spark‐ignition, automotive engine. The amount of exergy destroyed during the combustion process has been determined as functions of speed, load, equivalence ratio, start of combustion, combustion duration, combustion rate parameters, exhaust gas recirculation (EGR), inlet oxygen concentration, and compression ratio. In addition, design parameters that were examined included expansion ratio and the use of turbocharging. The fuels examined included isooctane (base), methane, propane, hexane, methanol, ethanol, hydrogen and carbon monoxide. For the part load base case (1400 rpm and a bmep of 325 kPa) using isooctane, the destruction of exergy was 20.8% of the fuel exergy. For many of the engine operating and design parameter changes, this destruction was relatively constant (between about 20 and 23%). The parameters that resulted in the greatest change of the exergy destruction were (1) equivalence ratio, (2) EGR, and (3) inlet oxygen concentration. For the base case conditions, the exergy destruction during the combustion process was different for the different fuels. The lowest destruction (8.1%) was for carbon monoxide and the highest destruction (20.8%) was for isooctane. The differences between the various fuels appear to relate to the complexity of the fuel molecule and the presence (or absence) of an oxygen atom. Copyright © 2011 John Wiley & Sons, Ltd.     

Availability analysis of a syngas fueled spark ignition engine using a multi-zone combustion model

A previously developed and validated zero-dimensional, multi-zone, thermodynamic combustion model for the prediction of spark ignition (SI) engine performance and nitric oxide (NO) emissions has been extended to include second-law analysis. The main characteristic of the model is the division of the burned gas into several distinct zones, in order to account for the temperature and chemical species stratification developed in the burned gas during combustion. Within the framework of the multi-zone model, the various availability components constituting the total availability of each of the multiple zones of the simulation are identified and calculated separately. The model is applied to a multi-cylinder, four-stroke, turbocharged and aftercooled, natural gas (NG) SI gas engine running on synthesis gas (syngas) fuel. The major part of the unburned mixture availability consists of the chemical contribution, ranging from 98% at the inlet valve closing (IVC) event to 83% at the ignition timing of the total availability for the 100% load case, which is due to the presence of the combustible fuel. On the contrary, the multiple burned zones possess mainly thermomechanical availability. Specifically, again for the 100% load case, the total availability of the first burned zone at the exhaust valve opening (EVO) event consists of thermomechanical availability approximately by 90%, with similar percentages for all other burned zones. Two definitions of the combustion exergetic efficiency are used to explore the degree of reversibility of the combustion process in each of the multiple burned zones. It is revealed that the crucial factor determining the thermodynamic perfection of combustion in each burned zone is the level of the temperatures at which combustion occurs in the zone, with minor influence of the whole temperature history of the zone during the complete combustion phase. The availability analysis is extended to various engine loads. The engine in question is supplied with increasingly leaner mixtures as loads rise in order to keep the emitted nitrogen oxides (NO_x) low. Therefore, in-cylinder combustion temperatures are reduced, resulting in increased destruction of availability due to combustion and reduced availability losses due to heat transfer with the cylinder walls, when expressed as percentages of the fuel chemical availability. Specifically, when engine load increases from 40% to 100% of full load, with the relative air–fuel ratio also increasing from 1.56 to 1.83, the destroyed availability due to combustion rises from 14.19% to 15.02% of the fuel chemical availability, while the respective percentage of the cumulative availability loss due to heat transfer decreases from 13.37% to 9.05%.     

Study of a Stirling engine used for domestic micro‐cogeneration. Thermodynamic analysis and experiment

One of the aims of this work is the study of the geometry of a micro‐cogenerator using a Stirling engine with four double effect pistons. The complex geometry of the heat exchangers was determined by optical measurements. Results of three thermodynamic models: Direct Method from Finite Speed Thermodynamics (FST), isothermal model (Schmidt), and adiabatic model (Finkelstein) are confronted to experimental ones. Direct Method consists of the study and the evaluation of the irreversibilities of thermal machines by analyzing the cycle, step by step, and directly integrating the equation of the First Law for processes with finite speed combined with Second Law of Thermodynamics, for each process of the cycle. The expression of efficiency and power, depending on the speed of the processes and geometric and functional parameters, is then obtained in a straightforward manner. The isothermal and adiabatic models are based on the division of Stirling engine in 3, respectively 5 control volumes, for which the ideal gas law and the equations of mass and energy balance are applied. Analysis of the process of heat transfer and flow of the working gas, taking place in the Stirling engine, is carried out taking into account instantaneous representation of the working fluid volume in the engine. A system of differential equations is solved by iteration using Matlab/Simulink software. The theoretical results are compared to experimental ones. This comparison allows to point out a good accuracy of the Direct Method and the Adiabatic Model, for the thermal operating parameters of the system, noting the different assumptions of each analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Combustion analysis of a spark ignition i. c. engine fuelled alternatively with natural gas and hydrogen-natural gas blends

This paper describes an experimental activity performed on a passenger car powered by a spark ignition engine fuelled alternatively with natural gas (CNG) and hydrogen-natural gas blends, with 15% (HCNG15) and 30% (HCNG30) of hydrogen by volume. The vehicle was tested on a chassis dynamometer over different driving cycles, allowing the investigation of more realistic operating conditions than those examined on an engine test bed at steady state conditions. Fuel consumption was estimated using the carbon balance methodology, allowing the comparison of engine average efficiency over the driving cycles for the tested fuels. Furthermore, cylinder pressure was measured and, by processing the pressure signal, a combustion analysis was performed allowing to estimate the burning rate and combustion phasing. Ignition timing was the same for all the tested fuels, in order to assess their interchangeability on in-use vehicles. Results showed CO₂ emission reduction between 3% and 6% for HCNG15 and between 13% and 16% for HCNG30 respect to natural gas. Fuel consumption in MJ/km did not show significant differences between CNG and HCNG15, while reductions between 3% and 7% have been observed with HCNG30. The heat release rate increased with hydrogen content in the blends, reaching values higher than those attained using CNG. The combustion duration, calculated as the angle between 10% and 90% of heat released, has been shortened, with 16% reduction for HCNG15 and 21% for HCNG30 respect to CNG at 2.5 bar imep and 2400 rpm. As a consequence, hydrogen addition resulted in a combustion phasing advance respect to CNG. Cycle-by-cycle variability decreased, particularly at low loads, due to the positive effect of hydrogen on combustion stability.     

Experimental analysis of a spark-ignition engine using exhaust gas recycle at WOT operation

Spark-ignition engines are still a competitive solution in a great number of applications. European manufacturers are all involved in the effort of improving fuel economy, at least at some engine operating points while meeting, of course, the pollutant emission standards.     

Research on the hot surface ignition of hydrogen‐air mixture under different influencing factors

To further reveal the pre‐ignition characteristics of hydrogen internal combustion engine, the effect of hot surface characteristic parameters on the ignition characteristics of hydrogen‐air mixture was investigated in this research. Based on the prototype of the constant volume combustion bomb with an overhead glow plug, the duration from the heating of the hot surface to the combustion of hydrogen‐air mixture, the so‐called heating duration, was firstly researched under different fuel‐air equivalence ratio, initial temperature, initial pressure, hot surface temperature, and hot surface area, and the influence of each factor on the heating duration was analyzed. The results show that the order of the effect of each factor on the hot surface ignition is as follows: hot surface temperature > initial pressure of hydrogen‐air mixture > equivalent ratio > initial temperature of hydrogen‐air mixture > hot surface area. The influence of the hot surface characteristic parameters on the heating duration was further analyzed in detail. On this basis, the relationship among the critical ignition temperature, the heating duration and the hot surface area was researched and established. The results show that the heating duration is the only major factor affecting the critical ignition temperature. Finally, the research results were applied to analysis the pre‐ignition in hydrogen internal combustion engine.     

Reduction of emissions in a biodiesel‐fueled compression ignition engine using exhaust gas recirculation and selective catalytic reduction techniques

This paper analyzes the emissions of a single‐cylinder diesel engine fueled with biodiesel, using selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) techniques. The aim of this paper is to compare both EGR and SCR techniques, which were studied under different brake powers. Grape seed biodiesel was used as a test fuel. Experiments were performed by both techniques at different loads and rates to find out the performance change in the engine and the change in the emission rates using both the techniques. Then the observations from both the techniques were compared, concluding that both the techniques show a sufficient reduction in NOx. Using the abovementioned techniques, a reduction in hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NOx), and smoke was observed. The EGR technique is more suitable for low‐load engine vehicles, as it affects the efficiency of the engine with an increase in the fuel consumption, whereas the SCR technique is suitable for high‐load engines, which do not affect the efficiency of the engine with a decrease in the fuel consumption.     

Development of online control system for elimination of backfire in a hydrogen fuelled spark ignition engine

Backfire is one of the major technical issues in a port injection type hydrogen fuelled spark ignition engine. It is an abnormal combustion phenomenon (pre-ignition) that takes place in combustion chamber and intake manifold during suction stroke. The flame propagates toward the upstream of the intake manifold from combustion chamber during backfire and thus can damage the intake and fuel supply systems of the engine, and stall the engine operation. The main cause of backfire could be the presence of any hot spot, lubricating oil particle's traces (HC and CO due to evaporation of the oil) and hot residual exhaust gas present in the combustion chamber during suction stroke which could act as an ignition source for fresh incoming charge. Monitoring the temperatures of the lubricating oil and exhaust gas during engine operation can reduce the probability of backfire. This was achieved by developing an electronic device which delays the injection timing of hydrogen fuel with the inputs of engine oil temperature (T_{lube oil}) and exhaust gas temperature (T_exh). It was observed from the experimental results that the threshold values of T_{lube oil} and T_exh were 85 °C and 540 °C respectively beyond which backfire occurred at equivalence ratio (φ) of 0.82. The developed device works based on the algorithm that retards the hydrogen injection to 40 ⁰aTDC whenever the temperatures (T_{lube oil} and T_exh) reached to the above mentioned values and thus the backfire was controlled. Delaying injection of hydrogen increased the time period at which only air is inducted during the early part of the suction stroke, this allows cooling of the available hot spots in the combustion chamber, hence the probability of backfire would be reduced.     

Thermodynamic optimization of Stirling heat engine with methane gas using finite speed thermodynamic model

With the daily rise in environmental issues due to the use of conventional fuels, researchers are motivated to use renewable energy sources. One of such waste heat and low-temperature differential driven energy sources is the Stirling engine. The performance of the Stirling engine can be improved by finding out the optimum operating and geometrical parameters with suitable working gas and thermal model. Based on this motivation, the current work focuses on the multiobjective optimization of the Stirling engine using the finite speed thermodynamic model and methane gas as the working fluid. Considering output power and pressure drop as two objective functions, the system is optimized using 11 geometrical and thermal design parameters. The optimization results are obtained in the form of the Pareto frontier. A sensitivity assessment is carried out to observe the decision variables, which are having a more sensitive effect on the optimization objectives. Optimization results reveal that 99.83% change in power output and 78% change in total pressure drop can take place in the two-dimensional optimization space. The optimal solution closest to the ideal solution has output power and pressure drop values as 12.31 kW and 22.76 kPa, respectively.     

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power is proposed and analyzed in this paper. Unlike a conventional organic Rankine cycle, a supercritical Rankine cycle does not go through the two-phase region during the heating process. By adopting zeotropic mixtures as the working fluids, the condensation process also happens non-isothermally. Both of these features create a potential for reducing the irreversibilities and improving the system efficiency. A comparative study between an organic Rankine cycle and the proposed supercritical Rankine cycle shows that the proposed cycle can achieve thermal efficiencies of 10.8-13.4% with the cycle high temperature of 393 K-473 K as compared to 9.7-10.1% for the organic Rankine cycle, which is an improvement of 10-30% over the organic Rankine cycle. When including the heating and condensation processes in the system, the system exergy efficiency is 38.6% for the proposed supercritical Rankine cycle as compared to 24.1% for the organic Rankine cycle.