The urban areas of Pakistan exhibit some of the world’s highest levels of air pollution, primaril... more The urban areas of Pakistan exhibit some of the world’s highest levels of air pollution, primarily due to sub-2.5 μm particulate emissions. This issue significantly impairs both the country’s economy and the quality of life of its residents. Road transport is a significant contributor to anthropogenic air pollution but there are discrepancies about the extent of its share. Source apportionment and sectoral inventory studies attribute anywhere between 5 and >80% of the total air pollution to vehicular sources. This uncertainty propagates into the transport policy interventions that are informed by such studies and can thus hinder the achievement of desired pollution mitigation targets. In an effort to reconcile such discrepancies and guide future studies and policy-making efforts, this paper critically reviews source apportionment studies conducted in the urban centres of Pakistan over the past two decades. The strengths and weaknesses of different approaches are compared, and res...
Forthcoming worldwide emissions regulations will start regulating ammonia emissions from light du... more Forthcoming worldwide emissions regulations will start regulating ammonia emissions from light duty vehicles. At present, most light duty vehicles are powered by gasoline spark ignition engines. Sources of ammonia emission from such engines can be in-cylinder reactions (i.e. combustion) or downstream reactions across aftertreatment devices, particularly three-way catalysts. The latter has been known to be a major source of ammonia emissions from gasoline vehicles and has been extensively investigated. The former (combustion), less so, and thus is the subject of this work. A two-zone thermodynamic spark ignition engine model with a comprehensive chemical kinetics framework (C3MechV3.3 mechanism), after being validated against experimental ammonia emissions data, is used to study ammonia formation during combustion. Reaction pathways responsible for its generation are analysed and the effects of changing the following engine operational and combustion parameters are explored: engine l...
We characterized the breaking, buckling and deformation of a liquid marble upon liquid exchange v... more We characterized the breaking, buckling and deformation of a liquid marble upon liquid exchange via external inflow and outflow. During liquid addition, the breaking of liquid marbles was affected by the existence of a swirl flow pattern. During liquid removal, the liquid marbles buckled and their morphology was controlled using penetrating pins. During a zero-net-flow perfusion process, the shapes of liquid marbles were controlled by the arrangement of the inlets and outlets.
Developing a reliable means of predicting and controlling engine operation at various operating c... more Developing a reliable means of predicting and controlling engine operation at various operating conditions may be a reasonable pathway for meeting increasingly stringent engine emission regulations. In order to do so, estimates of the mixture composition at the end of the gas exchange process (i.e. at exhaust port closure, or EPC) are helpful for having accurate models of engine combustion. A substantial fraction of the trapped charge mixture is composed of residual gases from previous cycles. This fraction, the trapped residual fraction, changes combustion characteristics of the trapped mixture. Residual gases dilute the fresh charge, thus decreasing the flame speed and temperature. Moreover, because of their spatial inhomogeneity, especially around the spark plug, these gases seem to have implications for engine stability. All these factors likely affect engine performance and emissions. Unfortunately, it is not practical to directly measure the trapped residual fraction for engin...
Gasoline engines employing the spatially distributed auto-ignition combustion mode, known as cont... more Gasoline engines employing the spatially distributed auto-ignition combustion mode, known as controlled auto-ignition (CAI), are a prospective technology for significantly improving engine efficiency and reducing emissions. This review paper provides an overview of developments in various gasoline CAI technologies and discusses their attendant strengths and weaknesses. Hybrid propulsion systems powered by high-efficiency gasoline CAI engines can provide a low-carbon pathway for mobility sector decarbonisation. Therefore, this paper focuses on the challenges and opportunities of CAI implementation, especially for electrified powertrains. Different control actuators that can extend the CAI operating range are discussed, and opportunities for synergistic operation between thermal and electric components of hybridised powertrains are identified. Such synergies can remove impediments in the way of CAI system adoption and can, thus, support CAI adoption and maximise efficiency gains from ...
Low temperature heat release (LTHR) has been of interest to researchers for its potential to miti... more Low temperature heat release (LTHR) has been of interest to researchers for its potential to mitigate knock in spark ignition (SI) engines and control auto-ignition in advanced compression ignition (ACI) engines. Previous studies have identified and investigated LTHR in both ACI and SI engines before the main high temperature heat release (HTHR) event by appropriately curating the in-cylinder thermal state during compression, or in the case of SI engines, timing the spark discharge late to reveal LTHR (sometimes referred to as pre-spark heat release). In this work, LTHR is demonstrated in isolation from HTHR events. Tests were run on motored single-cylinder engines and inlet air temperatures and pressures were adjusted to realise LTHR from n-heptane and iso-octane (2,2,4-trimethylpentane) without entering the HTHR regime. LTHR was observed for a lean n-heptane-air mixture at inlet temperatures ranging from 60°C to 100°C and inlet pressures of 0.9 bar (absolute). For temperatures bel...
The diagnostic merits of high-speed (HS) exhaust gas temperature and pressure measurements for in... more The diagnostic merits of high-speed (HS) exhaust gas temperature and pressure measurements for indexing engine stability and identifying abnormal combustion cycles are explored through experimental investigations on a low speed, single-cylinder engine. Exhaust temperature and pressure are measured using a fine wire 50 μm thermocouple and a piezoresistive pressure transducer, respectively. Synchronously recorded cylinder pressure data is used to continuously index combustion variations, and then anomalous combustion event detection and engine stability monitoring are attempted using HS exhaust temperature and pressure measurements. Two types of abnormal combustion cycles, namely, misfiring and overload cycles are used to typify low and high intensity anomalous combustion cycles, respectively. The results demonstrate that if suitable cyclic exhaust pressure and temperature metrics are used, anomalous combustion cycles can be identified, and overall combustion variability levels can be...
Gas exchange processes in two-stroke internal combustion engines, commonly referred to as scaveng... more Gas exchange processes in two-stroke internal combustion engines, commonly referred to as scavenging, are responsible for removing the exhaust gases in the combustion chamber and preparing the combustible fuel-oxidizer mixture that undergoes combustion and converts the chemical energy of the fuel into mechanical work. Scavenging is a complicated phenomenon because of the simultaneous introduction of fresh gases into the engine cylinder through the intake ports, and the expulsion of combustion products from the previous cycles through the exhaust ports. A non-negligible fraction of the gaseous mixture that is trapped in the cylinder at the conclusion of scavenging is composed of residual gases from the previous cycle. This can cause significant changes to the combustion characteristics of the mixture by changing its composition and temperature, i.e. its thermodynamic state. Thus, it is vital to have accurate knowledge of the thermodynamic state of the post-scavenging mixture to be ab...
ASME 2019 Internal Combustion Engine Division Fall Technical Conference
Gas exchange processes in two-stroke internal combustion engines, i.e. scavenging, remove exhaust... more Gas exchange processes in two-stroke internal combustion engines, i.e. scavenging, remove exhaust gases from the combustion chamber and prepare the fuel-oxidizer mixture that undergoes combustion. A non-negligible fraction of the mixture trapped in the cylinder at the conclusion of scavenging is composed of residual gases from the previous cycle. This can cause significant changes to the combustion characteristics of the mixture by changing its composition and temperature, i.e. its thermodynamic state. Thus, it is vital to have accurate knowledge of the thermodynamic state of the post-scavenging mixture to be able to reliably predict and control engine performance, efficiency and emissions. Several simple-scavenging models can be found in the literature that — based on a variety of idealized interaction modes between incoming and cylinder gases — calculate the state of the trapped mixture. In this study, boundary conditions extracted from a validated 1-D predictive model of a single...
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering
The chemical composition of the trapped fuel-air-residual gas mixture controls the nature of comb... more The chemical composition of the trapped fuel-air-residual gas mixture controls the nature of combustion in internal combustion engines and thus serves as a key determinant of the ensuing emissions and work production processes. A frequently used trapped composition metric for engine control is the trapped equivalence ratio. Unfortunately, in two-stroke engines, it is unfeasible to accurately determine this using traditional intake flow and exhaust emissions measurements because of the simultaneous occurrence of intake and exhaust processes, which causes: (1) exhaust emissions to be diluted by the slippage (short-circuiting) of fresh air through the exhaust ports, i.e., trapping inefficiencies, and (2) high residual combustion product retainment, i.e., scavenging inefficiencies. The current paper supplements scavenging efficiency data obtained in a previous study for a cross-scavenged, natural-gas, two-stroke engine with experimental trapping efficiency data from the same engine, and...
Changes in the flammability characteristics of a combusting mixture and its 'dilution&... more Changes in the flammability characteristics of a combusting mixture and its 'dilution' levels-characterized, respectively, by the mixture's equivalence ratio and residual gas fraction-can have significant impacts on the nature of combustion in internal combustion engines. These combustion changes can manifest as variations in combustion phasing and repeatability, and affect engine efficiency, emissions, and performance. The current work uses experimental, high-speed, in-cylinder CO 2 concentration data from a single-cylinder, natural gas-fueled engine to track compositional variations in the combusting mixture; and then uses a chemical kinetics solver to isolate the effects of flammability and dilution changes on the mixture's 'reactivity,' which is characterized by its laminar flame speed (LFS) and ignition delay (ID). It is found that LFS changes are driven strongly by the trapped equivalence ratio, while ID changes are driven primarily by dilution and pressure changes. Additionally, the effects of LFS changes on the overall combustion phasing are found to be more pronounced than those from ID changes, as the former influences both the combustion initiation and propagation processes.
ASME 2019 Internal Combustion Engine Division Fall Technical Conference, 2019
The increased production of natural gas harvested from unconventional sources, such as shale, has... more The increased production of natural gas harvested from unconventional sources, such as shale, has led to fluctuations in the species composition of natural gas moving through pipelines. These variations alter the chemical properties of the bulk gas mixture and, consequently, affect the operation of pipeline compressor engines which use the gas as fuel. Among several possible ramifications of these variations is that of unacceptably high engine-out NOx emissions. Therefore, engine controller enhancements which can account for fuel variability are necessary for maintaining emissions compliance. Having the means to predict NOx emissions from a field engine can inform the development of such control schemes. There are several types of compressor engines; however, this study considers a large bore, lean-burn, two-stroke, integral compressor engine. This class of engine has unique operating conditions which make the formation of engine-out NOx different from typical automotive spark-ignit...
Rate of heat release calculated for experimental and simulated pressures……………………………………………………………….... more Rate of heat release calculated for experimental and simulated pressures……………………………………………………………….. 49 Simulated and experimental cylinder pressures for one cycle………… 51 Simulated cylinder temperature for one cycle………………………… 52 (a) Mass flow rate in and out of the engine cylinder. (b) Experimental stuffing box and exhaust manifold pressure…………………………… 54 Mass of gases present in the engine cylinder………………………….. 55 Accumulated work for one complete engine cycle……………………. 57 Accumulated wall heat transfer during one complete engine cycle…… 58 Temperature-Specific entropy diagram for the current operating condition……………………………………………………………… 60 Total entropy as a function of crank angle for the current operating condition……………………………………………………………….. 61 Specific internal energy as a function of bulk gas temperature for the current operating condition……………………………………………. 63 Specific exergy as a function of bulk gas temperature for the current operating condition…………………………………………………… 63 Cylinder charge exergy vs. crank angle for one complete engine cycle at the current operating conditions. (i: expansion work, ii: irreversibility due to combustion, iii: irreversibility due to heat transfer, iv: exergy lost to exhaust, v: chemical exergy of the fuel)…... 65 Amount of fuel energy and exergy in kJ exhausted, destroyed and converted to work and heat transfer for the current operating condition……………………………………………………………….. 66 Percentage of fuel energy and exergy exhausted, destroyed and converted to work and heat transfer for the current operating condition……………………………………………………………….. 67 Percentage of fuel energy and exergy exhausted, destroyed and converted to work and heat transfer for (i) a four-stroke engine [23]
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2021
In internal combustion engines, the chemical composition of the trapped fuel-air-residual gas mix... more In internal combustion engines, the chemical composition of the trapped fuel-air-residual gas mixture controls the nature of combustion, which, in turn, determines the characteristics of the ensuing emissions and work production processes. Therefore, knowledge of the trapped mixture’s composition is critical for reliably predicting and controlling engine performance, emissions, and efficiency. A good index of the overall trapped mixture composition is the trapped equivalence ratio. Unfortunately, in two-stroke engines, it is unfeasible to accurately determine the trapped equivalence ratio using traditional intake flow measurements and exhaust emissions data. This limitation arises from the simultaneous occurrence of intake and exhaust processes in two-stroke engines, which causes: (1) exhaust emissions to be diluted by excess fresh air that was supplied for achieving effective gas exchange, that is trapping inefficiencies and (2) a significant fraction of combustion products to stay...
It is vital to have accurate predictions of the gas exchange behavior of an engine in order to re... more It is vital to have accurate predictions of the gas exchange behavior of an engine in order to reliably study engine performance and emissions using engine simulation models. There are a multitude of factors, both upstream and downstream of the engine cylinder, which influence its gas exchange characteristics. Quite often these influences are interconnected in a non-linear manner that results in complicated feedback loops, which can introduce significant errors in the computed thermodynamic state of the post-breathing cylinder mixture. The effects of such bi-directional movement of pressure pulses are particularly pronounced in two-stroke engines. This study investigates the importance of exhaust system design on the scavenging characteristics of a piston-scavenged, cross-flow, two-stroke engine. A validated one-dimensional predictive model is used to study the effects of changing the exhaust port timing, exhaust system length, and exhaust port efficiency on the breathing performanc...
The urban areas of Pakistan exhibit some of the world’s highest levels of air pollution, primaril... more The urban areas of Pakistan exhibit some of the world’s highest levels of air pollution, primarily due to sub-2.5 μm particulate emissions. This issue significantly impairs both the country’s economy and the quality of life of its residents. Road transport is a significant contributor to anthropogenic air pollution but there are discrepancies about the extent of its share. Source apportionment and sectoral inventory studies attribute anywhere between 5 and >80% of the total air pollution to vehicular sources. This uncertainty propagates into the transport policy interventions that are informed by such studies and can thus hinder the achievement of desired pollution mitigation targets. In an effort to reconcile such discrepancies and guide future studies and policy-making efforts, this paper critically reviews source apportionment studies conducted in the urban centres of Pakistan over the past two decades. The strengths and weaknesses of different approaches are compared, and res...
Forthcoming worldwide emissions regulations will start regulating ammonia emissions from light du... more Forthcoming worldwide emissions regulations will start regulating ammonia emissions from light duty vehicles. At present, most light duty vehicles are powered by gasoline spark ignition engines. Sources of ammonia emission from such engines can be in-cylinder reactions (i.e. combustion) or downstream reactions across aftertreatment devices, particularly three-way catalysts. The latter has been known to be a major source of ammonia emissions from gasoline vehicles and has been extensively investigated. The former (combustion), less so, and thus is the subject of this work. A two-zone thermodynamic spark ignition engine model with a comprehensive chemical kinetics framework (C3MechV3.3 mechanism), after being validated against experimental ammonia emissions data, is used to study ammonia formation during combustion. Reaction pathways responsible for its generation are analysed and the effects of changing the following engine operational and combustion parameters are explored: engine l...
We characterized the breaking, buckling and deformation of a liquid marble upon liquid exchange v... more We characterized the breaking, buckling and deformation of a liquid marble upon liquid exchange via external inflow and outflow. During liquid addition, the breaking of liquid marbles was affected by the existence of a swirl flow pattern. During liquid removal, the liquid marbles buckled and their morphology was controlled using penetrating pins. During a zero-net-flow perfusion process, the shapes of liquid marbles were controlled by the arrangement of the inlets and outlets.
Developing a reliable means of predicting and controlling engine operation at various operating c... more Developing a reliable means of predicting and controlling engine operation at various operating conditions may be a reasonable pathway for meeting increasingly stringent engine emission regulations. In order to do so, estimates of the mixture composition at the end of the gas exchange process (i.e. at exhaust port closure, or EPC) are helpful for having accurate models of engine combustion. A substantial fraction of the trapped charge mixture is composed of residual gases from previous cycles. This fraction, the trapped residual fraction, changes combustion characteristics of the trapped mixture. Residual gases dilute the fresh charge, thus decreasing the flame speed and temperature. Moreover, because of their spatial inhomogeneity, especially around the spark plug, these gases seem to have implications for engine stability. All these factors likely affect engine performance and emissions. Unfortunately, it is not practical to directly measure the trapped residual fraction for engin...
Gasoline engines employing the spatially distributed auto-ignition combustion mode, known as cont... more Gasoline engines employing the spatially distributed auto-ignition combustion mode, known as controlled auto-ignition (CAI), are a prospective technology for significantly improving engine efficiency and reducing emissions. This review paper provides an overview of developments in various gasoline CAI technologies and discusses their attendant strengths and weaknesses. Hybrid propulsion systems powered by high-efficiency gasoline CAI engines can provide a low-carbon pathway for mobility sector decarbonisation. Therefore, this paper focuses on the challenges and opportunities of CAI implementation, especially for electrified powertrains. Different control actuators that can extend the CAI operating range are discussed, and opportunities for synergistic operation between thermal and electric components of hybridised powertrains are identified. Such synergies can remove impediments in the way of CAI system adoption and can, thus, support CAI adoption and maximise efficiency gains from ...
Low temperature heat release (LTHR) has been of interest to researchers for its potential to miti... more Low temperature heat release (LTHR) has been of interest to researchers for its potential to mitigate knock in spark ignition (SI) engines and control auto-ignition in advanced compression ignition (ACI) engines. Previous studies have identified and investigated LTHR in both ACI and SI engines before the main high temperature heat release (HTHR) event by appropriately curating the in-cylinder thermal state during compression, or in the case of SI engines, timing the spark discharge late to reveal LTHR (sometimes referred to as pre-spark heat release). In this work, LTHR is demonstrated in isolation from HTHR events. Tests were run on motored single-cylinder engines and inlet air temperatures and pressures were adjusted to realise LTHR from n-heptane and iso-octane (2,2,4-trimethylpentane) without entering the HTHR regime. LTHR was observed for a lean n-heptane-air mixture at inlet temperatures ranging from 60°C to 100°C and inlet pressures of 0.9 bar (absolute). For temperatures bel...
The diagnostic merits of high-speed (HS) exhaust gas temperature and pressure measurements for in... more The diagnostic merits of high-speed (HS) exhaust gas temperature and pressure measurements for indexing engine stability and identifying abnormal combustion cycles are explored through experimental investigations on a low speed, single-cylinder engine. Exhaust temperature and pressure are measured using a fine wire 50 μm thermocouple and a piezoresistive pressure transducer, respectively. Synchronously recorded cylinder pressure data is used to continuously index combustion variations, and then anomalous combustion event detection and engine stability monitoring are attempted using HS exhaust temperature and pressure measurements. Two types of abnormal combustion cycles, namely, misfiring and overload cycles are used to typify low and high intensity anomalous combustion cycles, respectively. The results demonstrate that if suitable cyclic exhaust pressure and temperature metrics are used, anomalous combustion cycles can be identified, and overall combustion variability levels can be...
Gas exchange processes in two-stroke internal combustion engines, commonly referred to as scaveng... more Gas exchange processes in two-stroke internal combustion engines, commonly referred to as scavenging, are responsible for removing the exhaust gases in the combustion chamber and preparing the combustible fuel-oxidizer mixture that undergoes combustion and converts the chemical energy of the fuel into mechanical work. Scavenging is a complicated phenomenon because of the simultaneous introduction of fresh gases into the engine cylinder through the intake ports, and the expulsion of combustion products from the previous cycles through the exhaust ports. A non-negligible fraction of the gaseous mixture that is trapped in the cylinder at the conclusion of scavenging is composed of residual gases from the previous cycle. This can cause significant changes to the combustion characteristics of the mixture by changing its composition and temperature, i.e. its thermodynamic state. Thus, it is vital to have accurate knowledge of the thermodynamic state of the post-scavenging mixture to be ab...
ASME 2019 Internal Combustion Engine Division Fall Technical Conference
Gas exchange processes in two-stroke internal combustion engines, i.e. scavenging, remove exhaust... more Gas exchange processes in two-stroke internal combustion engines, i.e. scavenging, remove exhaust gases from the combustion chamber and prepare the fuel-oxidizer mixture that undergoes combustion. A non-negligible fraction of the mixture trapped in the cylinder at the conclusion of scavenging is composed of residual gases from the previous cycle. This can cause significant changes to the combustion characteristics of the mixture by changing its composition and temperature, i.e. its thermodynamic state. Thus, it is vital to have accurate knowledge of the thermodynamic state of the post-scavenging mixture to be able to reliably predict and control engine performance, efficiency and emissions. Several simple-scavenging models can be found in the literature that — based on a variety of idealized interaction modes between incoming and cylinder gases — calculate the state of the trapped mixture. In this study, boundary conditions extracted from a validated 1-D predictive model of a single...
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering
The chemical composition of the trapped fuel-air-residual gas mixture controls the nature of comb... more The chemical composition of the trapped fuel-air-residual gas mixture controls the nature of combustion in internal combustion engines and thus serves as a key determinant of the ensuing emissions and work production processes. A frequently used trapped composition metric for engine control is the trapped equivalence ratio. Unfortunately, in two-stroke engines, it is unfeasible to accurately determine this using traditional intake flow and exhaust emissions measurements because of the simultaneous occurrence of intake and exhaust processes, which causes: (1) exhaust emissions to be diluted by the slippage (short-circuiting) of fresh air through the exhaust ports, i.e., trapping inefficiencies, and (2) high residual combustion product retainment, i.e., scavenging inefficiencies. The current paper supplements scavenging efficiency data obtained in a previous study for a cross-scavenged, natural-gas, two-stroke engine with experimental trapping efficiency data from the same engine, and...
Changes in the flammability characteristics of a combusting mixture and its 'dilution&... more Changes in the flammability characteristics of a combusting mixture and its 'dilution' levels-characterized, respectively, by the mixture's equivalence ratio and residual gas fraction-can have significant impacts on the nature of combustion in internal combustion engines. These combustion changes can manifest as variations in combustion phasing and repeatability, and affect engine efficiency, emissions, and performance. The current work uses experimental, high-speed, in-cylinder CO 2 concentration data from a single-cylinder, natural gas-fueled engine to track compositional variations in the combusting mixture; and then uses a chemical kinetics solver to isolate the effects of flammability and dilution changes on the mixture's 'reactivity,' which is characterized by its laminar flame speed (LFS) and ignition delay (ID). It is found that LFS changes are driven strongly by the trapped equivalence ratio, while ID changes are driven primarily by dilution and pressure changes. Additionally, the effects of LFS changes on the overall combustion phasing are found to be more pronounced than those from ID changes, as the former influences both the combustion initiation and propagation processes.
ASME 2019 Internal Combustion Engine Division Fall Technical Conference, 2019
The increased production of natural gas harvested from unconventional sources, such as shale, has... more The increased production of natural gas harvested from unconventional sources, such as shale, has led to fluctuations in the species composition of natural gas moving through pipelines. These variations alter the chemical properties of the bulk gas mixture and, consequently, affect the operation of pipeline compressor engines which use the gas as fuel. Among several possible ramifications of these variations is that of unacceptably high engine-out NOx emissions. Therefore, engine controller enhancements which can account for fuel variability are necessary for maintaining emissions compliance. Having the means to predict NOx emissions from a field engine can inform the development of such control schemes. There are several types of compressor engines; however, this study considers a large bore, lean-burn, two-stroke, integral compressor engine. This class of engine has unique operating conditions which make the formation of engine-out NOx different from typical automotive spark-ignit...
Rate of heat release calculated for experimental and simulated pressures……………………………………………………………….... more Rate of heat release calculated for experimental and simulated pressures……………………………………………………………….. 49 Simulated and experimental cylinder pressures for one cycle………… 51 Simulated cylinder temperature for one cycle………………………… 52 (a) Mass flow rate in and out of the engine cylinder. (b) Experimental stuffing box and exhaust manifold pressure…………………………… 54 Mass of gases present in the engine cylinder………………………….. 55 Accumulated work for one complete engine cycle……………………. 57 Accumulated wall heat transfer during one complete engine cycle…… 58 Temperature-Specific entropy diagram for the current operating condition……………………………………………………………… 60 Total entropy as a function of crank angle for the current operating condition……………………………………………………………….. 61 Specific internal energy as a function of bulk gas temperature for the current operating condition……………………………………………. 63 Specific exergy as a function of bulk gas temperature for the current operating condition…………………………………………………… 63 Cylinder charge exergy vs. crank angle for one complete engine cycle at the current operating conditions. (i: expansion work, ii: irreversibility due to combustion, iii: irreversibility due to heat transfer, iv: exergy lost to exhaust, v: chemical exergy of the fuel)…... 65 Amount of fuel energy and exergy in kJ exhausted, destroyed and converted to work and heat transfer for the current operating condition……………………………………………………………….. 66 Percentage of fuel energy and exergy exhausted, destroyed and converted to work and heat transfer for the current operating condition……………………………………………………………….. 67 Percentage of fuel energy and exergy exhausted, destroyed and converted to work and heat transfer for (i) a four-stroke engine [23]
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2021
In internal combustion engines, the chemical composition of the trapped fuel-air-residual gas mix... more In internal combustion engines, the chemical composition of the trapped fuel-air-residual gas mixture controls the nature of combustion, which, in turn, determines the characteristics of the ensuing emissions and work production processes. Therefore, knowledge of the trapped mixture’s composition is critical for reliably predicting and controlling engine performance, emissions, and efficiency. A good index of the overall trapped mixture composition is the trapped equivalence ratio. Unfortunately, in two-stroke engines, it is unfeasible to accurately determine the trapped equivalence ratio using traditional intake flow measurements and exhaust emissions data. This limitation arises from the simultaneous occurrence of intake and exhaust processes in two-stroke engines, which causes: (1) exhaust emissions to be diluted by excess fresh air that was supplied for achieving effective gas exchange, that is trapping inefficiencies and (2) a significant fraction of combustion products to stay...
It is vital to have accurate predictions of the gas exchange behavior of an engine in order to re... more It is vital to have accurate predictions of the gas exchange behavior of an engine in order to reliably study engine performance and emissions using engine simulation models. There are a multitude of factors, both upstream and downstream of the engine cylinder, which influence its gas exchange characteristics. Quite often these influences are interconnected in a non-linear manner that results in complicated feedback loops, which can introduce significant errors in the computed thermodynamic state of the post-breathing cylinder mixture. The effects of such bi-directional movement of pressure pulses are particularly pronounced in two-stroke engines. This study investigates the importance of exhaust system design on the scavenging characteristics of a piston-scavenged, cross-flow, two-stroke engine. A validated one-dimensional predictive model is used to study the effects of changing the exhaust port timing, exhaust system length, and exhaust port efficiency on the breathing performanc...
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Papers by Abdullah Bajwa