Emiliano Pipitone | Università degli Studi di Palermo (original) (raw)
Papers by Emiliano Pipitone
Journal of Engineering for Gas Turbines and Power
In-cylinder expansion of internal combustion engines based on Diesel or Otto cycles cannot be com... more In-cylinder expansion of internal combustion engines based on Diesel or Otto cycles cannot be completely brought down to ambient pressure, causing a 20% theoretical energy loss. Several systems have been implemented to recover and use this energy such as turbocharging, turbomechanical and turbo-electrical compounding, or the implementation of Miller cycles. In all these cases however, the amount of energy recovered is limited allowing the engine to reach an overall efficiency incremental improvement between 4% and 9%. Implementing an adequately designed expander–generator unit could efficiently recover the unexpanded exhaust gas energy and improve efficiency. In this work, the application of the expander–generator unit to a hybrid propulsion vehicle is considered, where the onboard energy storage receives power produced by an expander–generator, which could hence be employed for vehicle propulsion through an electric drivetrain. Starting from these considerations, a simple but effec...
Energies
As is widely known, internal combustion engines are not able to complete the expansion process of... more As is widely known, internal combustion engines are not able to complete the expansion process of the gas inside the cylinder, causing theoretical energy losses in the order of 20%. Several systems and methods have been proposed and implemented to recover the unexpanded gas energy, such as turbocharging, which partially exploits this energy to compress the fresh intake charge, or turbo-mechanical and turbo-electrical compounding, where the amount of unexpanded gas energy not used by the compressor is dedicated to propulsion or is transformed into electric energy. In all of these cases, however, maximum efficiency improvements between 4% and 9% have been achieved. In this work, the authors deal with an alternative propulsion system composed of a CNG-fueled spark ignition engine equipped with a turbine-generator specifically dedicated to unexpanded exhaust gas energy recovery and with a separated electrically driven turbocompressor. The system was conceived specifically for hybrid pro...
SAE Technical Paper, 2008
It is known to internal combustion researcher that the correct determination of the crank positio... more It is known to internal combustion researcher that the correct determination of the crank position when the piston is at Top Dead Centre (TDC) is very important, since an error of 1 crank angle degree (CAD) can cause up to a 10% evaluation error on indicated mean effective ...
The results of previous experimental researches [1, 2] showed that great advantages can be achiev... more The results of previous experimental researches [1, 2] showed that great advantages can be achieved, both in terms of fuel consumption and pollutant emissions, in bi-fuel vehicles by means of the Double Fuel combustion, i.e. the simultaneous combustion of gasoline and a gaseous fuel, such as LPG or natural gas. The substantial increase in knock resistance pursued by adding LPG to gasoline, which allowed to maintain an overall stoichiometric proportion with air also at full load, is not documented in the scientific literature and induced the authors to perform a proper experimental campaign. The Motor Octane Number of LPG-gasoline mixtures has been hence determined on a standard CFR engine, equipped with a double fuel injection system in order to realize different proportions between the two fuels and electronically control the overall air-fuels mixture. The results of the measurement show a quadratic dependence of the Motor Octane Number (MON) of the mixture as function of the LPG c...
Sustainability
Global warming (GW) and urban pollution focused a great interest on hybrid electric vehicles (HEV... more Global warming (GW) and urban pollution focused a great interest on hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs) as cleaner alternatives to traditional internal combustion engine vehicles (ICEVs). The environmental impact related to the use of both ICEV and HEV mainly depends on the fossil fuel used by the thermal engines, while, in the case of the BEV, depends on the energy sources employed to produce electricity. Moreover, the production phase of each vehicle may also have a relevant environmental impact, due to the manufacturing processes and the materials employed. Starting from these considerations, the authors carried out a fair comparison of the environmental impact generated by three different vehicles characterized by different propulsion technology, i.e., an ICEV, an HEV, and a BEV, following the life cycle analysis methodology, i.e., taking into account five different environmental impact categories generated during all phases of the entire life of...
SAE Technical Paper Series
SAE Technical Paper Series
SAE Technical Paper Series
I n the ever increasing challenge of developing more efficient and less polluting engines, fricti... more I n the ever increasing challenge of developing more efficient and less polluting engines, friction reduction is of significant importance and its investigation needs an accurate and reliable measurement technique. The Pressurized Motoring method is one of the techniques used for both friction and heat transfer measurements in internal combustion engines. This method is able to simulate mechanical loading on the engine components similar to the fired conditions. It also allows measurement of friction mean effective pressure (FMEP) with a much smaller uncertainty as opposed to that achieved from a typical firing setup. Despite its advantages, the FMEP measurements obtained by this method are usually criticized over the fact that the thermal conditions imposed in pressurized motoring are far detached from those seen in fired conditions. In light of these considerations, the authors have put forward a modification to the method, employing Argon in place of Air as pressurization medium. Due to the higher heat capacity ratio, very high in-cylinder gas temperatures, possibly near to the fired conditions, can be achieved using Argon. This allowed better emulation of the fired engine and hence a more representative FMEP measurement. In this publication, experimental results obtained from a testing campaign with different Argon to Air concentration are presented. Tests were carried out on the fully instrumented test bench consisting of a direct-injection compression ignition, four cylinder engine, at different engine speeds and a peak in-cylinder pressure of 84bar. At each set point of speed, the Argon to Air concentration in the manifolds was varied to achieve different in-cylinder temperatures. The measured FMEP values, their uncertainty and their dependence on the different engine operating parameters are reported. It was found that the FMEP in the motored condition was not a function of peak in-cylinder temperature. This insensitivity to in-cylinder temperature further shows the advantage of the pressurized motored method. 2 EXPERIMENTAL INVESTIGATION ON THE USE OF ARGON TO IMPROVE FMEP DETERMINATION
SAE Technical Paper Series
Biofuel Research Journal
Please cite this article as: Pipitone E., Costanza A. An experimental investigation on the long-t... more Please cite this article as: Pipitone E., Costanza A. An experimental investigation on the long-term compatibility of preheated crude palm oil in a large compression ignition diesel engine.
Journal of Engineering for Gas Turbines and Power
The introduction of natural gas (NG) in the road transport market is proceeding through bifuel ve... more The introduction of natural gas (NG) in the road transport market is proceeding through bifuel vehicles, which, endowed of a double-injection system, can run either with gasoline or with NG. A third possibility is the simultaneous combustion of NG and gasoline, called double-fuel (DF) combustion: the addition of methane to gasoline allows to run the engine with stoichiometric air even at full load, without knocking phenomena, increasing engine efficiency of about 26% and cutting pollutant emissions by 90%. The introduction of DF combustion into series production vehicles requires, however, proper engine calibration (i.e., determination of DF injection and spark timing maps), a process which is drastically shortened by the use of computer simulations (with a 0D two zone approach for in-cylinder processes). An original knock onset prediction model is here proposed to be employed in zero-dimensional simulations for knock-safe performances optimization of engines fueled by gasoline-NG m...
Journal of Engineering for Gas Turbines and Power, 2017
Internal combustion engine development focuses mainly on two aspects: fuel economy improvement an... more Internal combustion engine development focuses mainly on two aspects: fuel economy improvement and pollutant emissions reduction. As a consequence, light duty spark ignition (SI) engines have become smaller, supercharged, and equipped with direct injection and advanced valve train control systems. The use of alternative fuels, such as natural gas (NG) and liquefied petroleum gas (LPG), thanks to their lower cost and environmental impact, widely spread in the automotive market, above all in bifuel vehicles, whose spark ignited engines may run either with gasoline or with gaseous fuel. The authors in previous works experimentally tested the strong engine efficiency increment and pollutant emissions reduction attainable by the simultaneous combustion of gasoline and gaseous fuel (NG or LPG). The increased knock resistance, obtained by the addition of gaseous fuel to gasoline, allowed the engine to run with stoichiometric mixture and best spark timing even at full load. In the present w...
Journal of Power Sources
Abstract In this two-part work, an electric kinetic energy recovery system (e-KERS) for internal ... more Abstract In this two-part work, an electric kinetic energy recovery system (e-KERS) for internal combustion engine vehicle (ICEV) is presented and its performance evaluated through numerical simulations. The KERS proposed is based on the use of a supercapacitor as energy storage, interfaced to a brushless machine through a properly designed power converter. In Part 1, the system is described and analysed, and the mathematical model used for the simulations is presented. For each component of the KERS, the real efficiency and the power or energy limitations are adequately considered. In Part 2, the energetic and economic advantages attainable by the proposed KERS are evaluated using MATLAB Simulink, considering a widely diffused passenger car and two reference driving cycles (ECE-15 and Artemis urban). Energy savings of the order of 20% were found, with a slight increase in vehicle weight (+2%) and with an overall commercial cost that would be compensated in 5 years thanks to the fuel economy improvement, to which corresponds an equal reduction of CO2 emissions. The low complexity of the system, never proposed for ICEV, the moderate weight of its components, and their availability on the market, make the solution presented ready for the introduction in current vehicle production.
Gaseous fuels, such as Liquefied Petroleum Gas (LPG) and Natural Gas (NG), thanks to their excell... more Gaseous fuels, such as Liquefied Petroleum Gas (LPG) and Natural Gas (NG), thanks to their excellent mixing capabilities and high knocking resistance, allow complete and cleaner combustion than gasoline in Spark Ignition (SI) engines, resulting in lower pollutant emissions, above all if particulate matter is considered. In previous works [1,2] the authors proved how the simultaneous combustion of gasoline and gaseous fuel (NG or LPG) may strongly reduce both fuel consumption and pollutant emissions with respect to pure gasoline operation without a significant power loss. These very encouraging results were obtained thanks to the strong knock resistance increase obtained adding gaseous fuel to gasoline, which allowed the use of stoichiometric mixtures and better spark advances, even at full load. The introduction of such a kind of combustion in series production engines would however require the use of properly calibrated simulation models, capable to adequately predict the performance and efficiency of engines fuelled by gaseous fuel-gasoline mixtures; in particular, specific combustion models are needed, together with reliable knock onset prediction sub-model. The total absence of such sub-models in the scientific literature induced the authors to investigate the knocking resistance of gasoline-propane mixtures and calibrate a proper knock onset prediction sub-model to be implemented in the zero dimensional thermodynamic models usually employed for engine performance optimization. To this purpose several light knocking in-cylinder pressure cycles have been recorded on a CFR engine, fuelled by gasoline, propane and their mixtures, varying the most important knock-related parameters: compression ratio, spark advance, inlet mixture temperature and fuel mixture composition. The collected data have been used to calibrate two different models, compared in terms of knock onset prediction accuracy: the Knock Integral model (KI) and the Ignition Delay model (ID). Both models revealed a good reliability in predicting the onset of knocking phenomena, with maximum errors around 4 crank angle degrees. The Knock Integral model showed a slightly higher accuracy, which, together with its lower computational effort, makes it preferable for the implementation in the commonly employed thermodynamic engine models.
In the last decade, gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), wi... more In the last decade, gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), widely spread in many countries, thanks to their prerogative of low cost and reduced environmental impact. Hence, bi-fuel engines, which allow to run either with gasoline or with gas (LPG or NG), became very popular. Moreover, as experimentally demonstrated by the authors in the previous works, these engines may also be fueled by a mixture of gasoline and gas, which, due to the high knock resistance of gas, allow to use stoichiometric mixtures also at full load, thus drastically improving engine efficiency and pollutant emissions with respect to pure gasoline operation without noticeable power loss. This third operation mode, called double fuel combustion, can be easily introduced in series production engine, since a simple electronic control unit (ECU) programing is required. The introduction into series production would require the availability of proper models for thermodynamic simulations, nowadays widely adopted to reduce research and development efforts and costs. To this purpose, the authors developed a quite original knock onset prediction model for knock-safe performances optimization of engines fueled by propane, gasoline, and their mixtures. The ignition delay model has been properly modified to account for the negative temperature coefficient (NTC) behavior exhibited by many hydrocarbon fuels such as gasoline and propane. The model parameters have been tuned by means of a considerable amount of light knocking in-cylinder pressure cycles acquired on a modified cooperative fuel research (CFR) engine, fueled by gasoline–propane mixtures. The adoption of many different compression ratios (CRs), inlet mixture temperatures, spark advances (SAs), and fuel mixture compositions allowed to use a very differentiated set of pressure and temperature curve, which gives the calibrated model a general validity for using different kinds of engines, i.e., naturally aspirated or supercharged. As a result, the model features a maximum knock onset prediction error around four crank angle degrees (CAD) and a mean absolute error always lower than 1 CAD, which is a negligible quantity from an engine control standpoint.
Gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), thanks to their good m... more Gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), thanks to their good mixing capabilities, allow complete and cleaner combustion than gasoline in spark ignition (SI) engines, resulting in lower pollutant emissions and particulate matter. In a previous work the authors showed that the simultaneous combustion of gasoline and LPG improves an SI engine efficiency with respect to pure gasoline operation with any significant power loss. The addition of LPG to the gasoline-air mixture produces an increase in knock resistance that allows running the engine at full load with overall stoichiometric mixture
and better spark advance. In order to predict both performance and efficiency of engines fed by LPG-gasoline mixtures, a specific combustion model and in particular a knock prediction
sub-model is required. Due to the lack of literature works about this matter, the authors investigated the knock resistance of LPG-gasoline mixtures. As a result, a reliable knock prediction sub-model has been obtained. The model can be easily implemented in thermodynamic simulations for a knock-safe engine performance optimization. The authors recorded light knocking in-cylinder pressure cycles on a cooperative fuel research (CFR) engine fueled by LPG-gasoline mixtures in different proportions. The tests were performed varying the compression ratio, the spark advance, and the inlet mixture temperature. The collected data have been used to calibrate and then compare two classical knock-prediction models. The models have been calibrated with a heterogeneous set of experimental data in order to predict knock occurrence in SI engines of different kinds. The results show that
the models predict the knock onset position with a maximum error of around 6 crank angle degrees (CAD).
Pollutant emissions reduction and energy saving policies increased the production of Spark Igniti... more Pollutant emissions reduction and energy saving policies increased the production of Spark Ignition (SI) engines operated with gaseous fuels. Natural Gas (NG) and Liquefied Petroleum Gas (LPG), thanks to their low cost and low environmental impact represent the best alternative. Bi-fuel engines, which may run either with gasoline or with gas (NG or LPG), widely spread in many countries thanks to their versatility, high efficiency and low pollutant emissions: gas fueled vehicles, as example, are allowed to run in many limited traffic zones. In the last years, supercharged SI engines fueled with either gasoline or gaseous fuel, spread in the market. Thermodynamic simulations, widely used to reduce costs during engine development and optimization process, require proper combustion and knock onset prediction models. In particular the fuel knocking resistance is a crucial issue in supercharged engines development. Starting from these considerations the authors developed and calibrated an original knock onset prediction model for knock-safe performances optimization of engines fueled by gasoline and gaseous fuels. The proposed model, despite its very simple formulation, takes into account the Negative Temperature Coefficient (NTC) behavior exhibited by many hydrocarbons fuels such as gasoline, propane and methane. The knock prediction model has been calibrated by a great number of light-knocking pressure cycles sampled using a Cooperative Fuel Research (CFR) engine. The engine Compression Ratio (CR), inlet mixture temperature and spark advance have been varied to obtain very different operative conditions for model calibration; as a result the model can be used in the development of different kind of engines, i.e. naturally aspirated or supercharged. Five fuels have been tested: gasoline, LPG, NG, propane and methane. The calibrated model showed a very high reliability with a maximum knock onset prediction error of only 4 crank angle degrees (CAD) and an overall mean absolute error lower than 1 CAD, that are negligible quantities from an engine control point of view.
Journal of Engineering for Gas Turbines and Power
In-cylinder expansion of internal combustion engines based on Diesel or Otto cycles cannot be com... more In-cylinder expansion of internal combustion engines based on Diesel or Otto cycles cannot be completely brought down to ambient pressure, causing a 20% theoretical energy loss. Several systems have been implemented to recover and use this energy such as turbocharging, turbomechanical and turbo-electrical compounding, or the implementation of Miller cycles. In all these cases however, the amount of energy recovered is limited allowing the engine to reach an overall efficiency incremental improvement between 4% and 9%. Implementing an adequately designed expander–generator unit could efficiently recover the unexpanded exhaust gas energy and improve efficiency. In this work, the application of the expander–generator unit to a hybrid propulsion vehicle is considered, where the onboard energy storage receives power produced by an expander–generator, which could hence be employed for vehicle propulsion through an electric drivetrain. Starting from these considerations, a simple but effec...
Energies
As is widely known, internal combustion engines are not able to complete the expansion process of... more As is widely known, internal combustion engines are not able to complete the expansion process of the gas inside the cylinder, causing theoretical energy losses in the order of 20%. Several systems and methods have been proposed and implemented to recover the unexpanded gas energy, such as turbocharging, which partially exploits this energy to compress the fresh intake charge, or turbo-mechanical and turbo-electrical compounding, where the amount of unexpanded gas energy not used by the compressor is dedicated to propulsion or is transformed into electric energy. In all of these cases, however, maximum efficiency improvements between 4% and 9% have been achieved. In this work, the authors deal with an alternative propulsion system composed of a CNG-fueled spark ignition engine equipped with a turbine-generator specifically dedicated to unexpanded exhaust gas energy recovery and with a separated electrically driven turbocompressor. The system was conceived specifically for hybrid pro...
SAE Technical Paper, 2008
It is known to internal combustion researcher that the correct determination of the crank positio... more It is known to internal combustion researcher that the correct determination of the crank position when the piston is at Top Dead Centre (TDC) is very important, since an error of 1 crank angle degree (CAD) can cause up to a 10% evaluation error on indicated mean effective ...
The results of previous experimental researches [1, 2] showed that great advantages can be achiev... more The results of previous experimental researches [1, 2] showed that great advantages can be achieved, both in terms of fuel consumption and pollutant emissions, in bi-fuel vehicles by means of the Double Fuel combustion, i.e. the simultaneous combustion of gasoline and a gaseous fuel, such as LPG or natural gas. The substantial increase in knock resistance pursued by adding LPG to gasoline, which allowed to maintain an overall stoichiometric proportion with air also at full load, is not documented in the scientific literature and induced the authors to perform a proper experimental campaign. The Motor Octane Number of LPG-gasoline mixtures has been hence determined on a standard CFR engine, equipped with a double fuel injection system in order to realize different proportions between the two fuels and electronically control the overall air-fuels mixture. The results of the measurement show a quadratic dependence of the Motor Octane Number (MON) of the mixture as function of the LPG c...
Sustainability
Global warming (GW) and urban pollution focused a great interest on hybrid electric vehicles (HEV... more Global warming (GW) and urban pollution focused a great interest on hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs) as cleaner alternatives to traditional internal combustion engine vehicles (ICEVs). The environmental impact related to the use of both ICEV and HEV mainly depends on the fossil fuel used by the thermal engines, while, in the case of the BEV, depends on the energy sources employed to produce electricity. Moreover, the production phase of each vehicle may also have a relevant environmental impact, due to the manufacturing processes and the materials employed. Starting from these considerations, the authors carried out a fair comparison of the environmental impact generated by three different vehicles characterized by different propulsion technology, i.e., an ICEV, an HEV, and a BEV, following the life cycle analysis methodology, i.e., taking into account five different environmental impact categories generated during all phases of the entire life of...
SAE Technical Paper Series
SAE Technical Paper Series
SAE Technical Paper Series
I n the ever increasing challenge of developing more efficient and less polluting engines, fricti... more I n the ever increasing challenge of developing more efficient and less polluting engines, friction reduction is of significant importance and its investigation needs an accurate and reliable measurement technique. The Pressurized Motoring method is one of the techniques used for both friction and heat transfer measurements in internal combustion engines. This method is able to simulate mechanical loading on the engine components similar to the fired conditions. It also allows measurement of friction mean effective pressure (FMEP) with a much smaller uncertainty as opposed to that achieved from a typical firing setup. Despite its advantages, the FMEP measurements obtained by this method are usually criticized over the fact that the thermal conditions imposed in pressurized motoring are far detached from those seen in fired conditions. In light of these considerations, the authors have put forward a modification to the method, employing Argon in place of Air as pressurization medium. Due to the higher heat capacity ratio, very high in-cylinder gas temperatures, possibly near to the fired conditions, can be achieved using Argon. This allowed better emulation of the fired engine and hence a more representative FMEP measurement. In this publication, experimental results obtained from a testing campaign with different Argon to Air concentration are presented. Tests were carried out on the fully instrumented test bench consisting of a direct-injection compression ignition, four cylinder engine, at different engine speeds and a peak in-cylinder pressure of 84bar. At each set point of speed, the Argon to Air concentration in the manifolds was varied to achieve different in-cylinder temperatures. The measured FMEP values, their uncertainty and their dependence on the different engine operating parameters are reported. It was found that the FMEP in the motored condition was not a function of peak in-cylinder temperature. This insensitivity to in-cylinder temperature further shows the advantage of the pressurized motored method. 2 EXPERIMENTAL INVESTIGATION ON THE USE OF ARGON TO IMPROVE FMEP DETERMINATION
SAE Technical Paper Series
Biofuel Research Journal
Please cite this article as: Pipitone E., Costanza A. An experimental investigation on the long-t... more Please cite this article as: Pipitone E., Costanza A. An experimental investigation on the long-term compatibility of preheated crude palm oil in a large compression ignition diesel engine.
Journal of Engineering for Gas Turbines and Power
The introduction of natural gas (NG) in the road transport market is proceeding through bifuel ve... more The introduction of natural gas (NG) in the road transport market is proceeding through bifuel vehicles, which, endowed of a double-injection system, can run either with gasoline or with NG. A third possibility is the simultaneous combustion of NG and gasoline, called double-fuel (DF) combustion: the addition of methane to gasoline allows to run the engine with stoichiometric air even at full load, without knocking phenomena, increasing engine efficiency of about 26% and cutting pollutant emissions by 90%. The introduction of DF combustion into series production vehicles requires, however, proper engine calibration (i.e., determination of DF injection and spark timing maps), a process which is drastically shortened by the use of computer simulations (with a 0D two zone approach for in-cylinder processes). An original knock onset prediction model is here proposed to be employed in zero-dimensional simulations for knock-safe performances optimization of engines fueled by gasoline-NG m...
Journal of Engineering for Gas Turbines and Power, 2017
Internal combustion engine development focuses mainly on two aspects: fuel economy improvement an... more Internal combustion engine development focuses mainly on two aspects: fuel economy improvement and pollutant emissions reduction. As a consequence, light duty spark ignition (SI) engines have become smaller, supercharged, and equipped with direct injection and advanced valve train control systems. The use of alternative fuels, such as natural gas (NG) and liquefied petroleum gas (LPG), thanks to their lower cost and environmental impact, widely spread in the automotive market, above all in bifuel vehicles, whose spark ignited engines may run either with gasoline or with gaseous fuel. The authors in previous works experimentally tested the strong engine efficiency increment and pollutant emissions reduction attainable by the simultaneous combustion of gasoline and gaseous fuel (NG or LPG). The increased knock resistance, obtained by the addition of gaseous fuel to gasoline, allowed the engine to run with stoichiometric mixture and best spark timing even at full load. In the present w...
Journal of Power Sources
Abstract In this two-part work, an electric kinetic energy recovery system (e-KERS) for internal ... more Abstract In this two-part work, an electric kinetic energy recovery system (e-KERS) for internal combustion engine vehicle (ICEV) is presented and its performance evaluated through numerical simulations. The KERS proposed is based on the use of a supercapacitor as energy storage, interfaced to a brushless machine through a properly designed power converter. In Part 1, the system is described and analysed, and the mathematical model used for the simulations is presented. For each component of the KERS, the real efficiency and the power or energy limitations are adequately considered. In Part 2, the energetic and economic advantages attainable by the proposed KERS are evaluated using MATLAB Simulink, considering a widely diffused passenger car and two reference driving cycles (ECE-15 and Artemis urban). Energy savings of the order of 20% were found, with a slight increase in vehicle weight (+2%) and with an overall commercial cost that would be compensated in 5 years thanks to the fuel economy improvement, to which corresponds an equal reduction of CO2 emissions. The low complexity of the system, never proposed for ICEV, the moderate weight of its components, and their availability on the market, make the solution presented ready for the introduction in current vehicle production.
Gaseous fuels, such as Liquefied Petroleum Gas (LPG) and Natural Gas (NG), thanks to their excell... more Gaseous fuels, such as Liquefied Petroleum Gas (LPG) and Natural Gas (NG), thanks to their excellent mixing capabilities and high knocking resistance, allow complete and cleaner combustion than gasoline in Spark Ignition (SI) engines, resulting in lower pollutant emissions, above all if particulate matter is considered. In previous works [1,2] the authors proved how the simultaneous combustion of gasoline and gaseous fuel (NG or LPG) may strongly reduce both fuel consumption and pollutant emissions with respect to pure gasoline operation without a significant power loss. These very encouraging results were obtained thanks to the strong knock resistance increase obtained adding gaseous fuel to gasoline, which allowed the use of stoichiometric mixtures and better spark advances, even at full load. The introduction of such a kind of combustion in series production engines would however require the use of properly calibrated simulation models, capable to adequately predict the performance and efficiency of engines fuelled by gaseous fuel-gasoline mixtures; in particular, specific combustion models are needed, together with reliable knock onset prediction sub-model. The total absence of such sub-models in the scientific literature induced the authors to investigate the knocking resistance of gasoline-propane mixtures and calibrate a proper knock onset prediction sub-model to be implemented in the zero dimensional thermodynamic models usually employed for engine performance optimization. To this purpose several light knocking in-cylinder pressure cycles have been recorded on a CFR engine, fuelled by gasoline, propane and their mixtures, varying the most important knock-related parameters: compression ratio, spark advance, inlet mixture temperature and fuel mixture composition. The collected data have been used to calibrate two different models, compared in terms of knock onset prediction accuracy: the Knock Integral model (KI) and the Ignition Delay model (ID). Both models revealed a good reliability in predicting the onset of knocking phenomena, with maximum errors around 4 crank angle degrees. The Knock Integral model showed a slightly higher accuracy, which, together with its lower computational effort, makes it preferable for the implementation in the commonly employed thermodynamic engine models.
In the last decade, gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), wi... more In the last decade, gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), widely spread in many countries, thanks to their prerogative of low cost and reduced environmental impact. Hence, bi-fuel engines, which allow to run either with gasoline or with gas (LPG or NG), became very popular. Moreover, as experimentally demonstrated by the authors in the previous works, these engines may also be fueled by a mixture of gasoline and gas, which, due to the high knock resistance of gas, allow to use stoichiometric mixtures also at full load, thus drastically improving engine efficiency and pollutant emissions with respect to pure gasoline operation without noticeable power loss. This third operation mode, called double fuel combustion, can be easily introduced in series production engine, since a simple electronic control unit (ECU) programing is required. The introduction into series production would require the availability of proper models for thermodynamic simulations, nowadays widely adopted to reduce research and development efforts and costs. To this purpose, the authors developed a quite original knock onset prediction model for knock-safe performances optimization of engines fueled by propane, gasoline, and their mixtures. The ignition delay model has been properly modified to account for the negative temperature coefficient (NTC) behavior exhibited by many hydrocarbon fuels such as gasoline and propane. The model parameters have been tuned by means of a considerable amount of light knocking in-cylinder pressure cycles acquired on a modified cooperative fuel research (CFR) engine, fueled by gasoline–propane mixtures. The adoption of many different compression ratios (CRs), inlet mixture temperatures, spark advances (SAs), and fuel mixture compositions allowed to use a very differentiated set of pressure and temperature curve, which gives the calibrated model a general validity for using different kinds of engines, i.e., naturally aspirated or supercharged. As a result, the model features a maximum knock onset prediction error around four crank angle degrees (CAD) and a mean absolute error always lower than 1 CAD, which is a negligible quantity from an engine control standpoint.
Gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), thanks to their good m... more Gaseous fuels, such as liquefied petroleum gas (LPG) and natural gas (NG), thanks to their good mixing capabilities, allow complete and cleaner combustion than gasoline in spark ignition (SI) engines, resulting in lower pollutant emissions and particulate matter. In a previous work the authors showed that the simultaneous combustion of gasoline and LPG improves an SI engine efficiency with respect to pure gasoline operation with any significant power loss. The addition of LPG to the gasoline-air mixture produces an increase in knock resistance that allows running the engine at full load with overall stoichiometric mixture
and better spark advance. In order to predict both performance and efficiency of engines fed by LPG-gasoline mixtures, a specific combustion model and in particular a knock prediction
sub-model is required. Due to the lack of literature works about this matter, the authors investigated the knock resistance of LPG-gasoline mixtures. As a result, a reliable knock prediction sub-model has been obtained. The model can be easily implemented in thermodynamic simulations for a knock-safe engine performance optimization. The authors recorded light knocking in-cylinder pressure cycles on a cooperative fuel research (CFR) engine fueled by LPG-gasoline mixtures in different proportions. The tests were performed varying the compression ratio, the spark advance, and the inlet mixture temperature. The collected data have been used to calibrate and then compare two classical knock-prediction models. The models have been calibrated with a heterogeneous set of experimental data in order to predict knock occurrence in SI engines of different kinds. The results show that
the models predict the knock onset position with a maximum error of around 6 crank angle degrees (CAD).
Pollutant emissions reduction and energy saving policies increased the production of Spark Igniti... more Pollutant emissions reduction and energy saving policies increased the production of Spark Ignition (SI) engines operated with gaseous fuels. Natural Gas (NG) and Liquefied Petroleum Gas (LPG), thanks to their low cost and low environmental impact represent the best alternative. Bi-fuel engines, which may run either with gasoline or with gas (NG or LPG), widely spread in many countries thanks to their versatility, high efficiency and low pollutant emissions: gas fueled vehicles, as example, are allowed to run in many limited traffic zones. In the last years, supercharged SI engines fueled with either gasoline or gaseous fuel, spread in the market. Thermodynamic simulations, widely used to reduce costs during engine development and optimization process, require proper combustion and knock onset prediction models. In particular the fuel knocking resistance is a crucial issue in supercharged engines development. Starting from these considerations the authors developed and calibrated an original knock onset prediction model for knock-safe performances optimization of engines fueled by gasoline and gaseous fuels. The proposed model, despite its very simple formulation, takes into account the Negative Temperature Coefficient (NTC) behavior exhibited by many hydrocarbons fuels such as gasoline, propane and methane. The knock prediction model has been calibrated by a great number of light-knocking pressure cycles sampled using a Cooperative Fuel Research (CFR) engine. The engine Compression Ratio (CR), inlet mixture temperature and spark advance have been varied to obtain very different operative conditions for model calibration; as a result the model can be used in the development of different kind of engines, i.e. naturally aspirated or supercharged. Five fuels have been tested: gasoline, LPG, NG, propane and methane. The calibrated model showed a very high reliability with a maximum knock onset prediction error of only 4 crank angle degrees (CAD) and an overall mean absolute error lower than 1 CAD, that are negligible quantities from an engine control point of view.