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Stefano Frigo

University of Pisa, DESTEC (Department of Energy, Systems, Territory and Construction Engineering), Faculty Member

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Stefano Frigo born in Lucca (Italy) the 06/14/1964.
He took a Bachelor Degree in Mechanical Engineering in 1991 at the University of Pisa and a Ph.D. in Energetic at the University of Genoa in 1994. From 1998 he belongs to the research staff of DESTEC (Department of Energy, System, Territory and Construction Engineering) of Pisa University, carrying on experimental activities in the field of internal combustion engines and biomass utilization in cogeneration power plants.
Stefano Frigo is co-inventor of 2 patents and author or co-author of more than 60 papers concerning:
- innovative fuel injection systems for two-stroke engines;
- fuel spray visualisation and analysis;
- utilisation of alternative fuels in internal combustion engines;
- biomass utilisation for energy production.

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Papers by Stefano Frigo

Development of a new steady state zero-dimensional simulation model for woody biomass gasification in a full scale plant

by Stefano Frigo and Roberto Gabbrielli

Energy Conversion and Management, 2016

A new steady state zero-dimensional simulation model for a full-scale woody biomass gasification ... more A new steady state zero-dimensional simulation model for a full-scale woody biomass gasification plant with fixed-bed downdraft gasifier has been developed using Aspen Plus Ò . The model includes the technical characteristics of all the components (gasifier, cyclone, exchangers, piping, etc.) of the plant and works in accordance with its actual main control logics. Simulation results accord with those obtained during an extensive experimental activity. After the model validation, the influence of operating parameters such as the equivalent ratio, the biomass moisture content and the gasifying air temperature on syngas composition have been analyzed in order to assess the operative behavior and the energy performance of the experimental plant. By recovering the sensible heat of the syngas at the outlet of the gasifier, it is possible to obtain higher values of the gasifying air temperature and an improvement of the overall gasification performances.

Electric Turbo Compounding Applied to a CI Engine: A Numerical Evaluation of Different Layouts

ASME 2016 Internal Combustion Engine Fall Technical Conference, 2016

At present, the application of turbocharging in compression ignition (CI) engines represents almo... more At present, the application of turbocharging in compression ignition (CI) engines represents almost all of the applications, especially for transportation where fuel efficiency and low emissions are the main targets. Following this approach, the possibility to couple an electric drive to the turbocharger (electric turbo compound, ETC) to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world.

Mathematical modelling and energy performance assessment of air impingement drying systems for the production of tissue paper

by Stefano Frigo and Roberto Gabbrielli

Energy, 2016

In this paper an original and exhaustive mathematical modelling of air impingement drying systems... more In this paper an original and exhaustive mathematical modelling of air impingement drying systems for the production of tissue paper in the Yankee-hoods configurations is reported, which offers the possibility to optimize its energy performance. The model takes into account many detailed operative parameters of the overall drying process with the aim to execute its energy and mass balance and to evaluate its energy performances. The validity of the mathematical model has been assessed by comparison with actual data from an existing tissue paper mill. Finally, the energy performances of two different layouts of the air system have been evaluated and compared. Changing the operative parameters of the drying process, such as air jet temperature and speed and moisture content of the extraction air, it is possible to obtain the same paper production with an energy saving of about 4.5%. In average, the layout with two parallel air circuits assure an energy saving of about 1% with respect to the layout with a single air circuit.

Development of a pumpless air-assisted injection system for two-cycle, S.I. engines

Sae Transactions, 1994

Further insight on ATAC and GDI combination in two-stroke engines

Sae Transactions, 2000

In two-stroke S.I. engines, direct fuel injection prevents fuel loss from the exhaust port, since... more In two-stroke S.I. engines, direct fuel injection prevents fuel loss from the exhaust port, since only air is employed for the scavenging process. However, to solve the problem of combustion irregularity at light loads due to excessive presence of residual gas in the charge, fuel injection should also produce charge stratification.

Numerical Comparison of an Electric Turbo Compound Applied to a SI and a CI Engine

Volume 2: Emissions Control Systems; Instrumentation, Controls, and Hybrids; Numerical Simulation; Engine Design and Mechanical Development, 2015

In a medium term scenario Internal Combustion Engine (ICE) downsizing and hybrid powertrain will ... more In a medium term scenario Internal Combustion Engine (ICE) downsizing and hybrid powertrain will represent the actual trend in vehicle technology to reduce fuel consumption and CO 2 emission. Concerning downsizing concept, to maintain a reasonable power level in small engines, the application of turbocharging is mandatory both for spark ignition (SI) and compression ignition (CI) engines. Following this aspect, the possibility to couple an electric machine to the turbocharger (electric turbo compound, ETC) to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world and by the current application in the F1 Championship. The present paper shows the first numerical results of a research program focused on the comparison of the benefits resulting from the application of an ETC to a small twincylinder SI engine (900 cm 3 ) and to a four cylinders CI engine (1600 cm 3 ), both of the same maximum power. Starting from the experimental maps of several turbines and compressors, complete model of both turbocharged engines were created using the AVL BOOST one-dimension code. Concerning the SI engine, first numerical results show that ETC can improve the average overall efficiency at the highest engine speeds and loads. Besides, boost range extension in the lowest engine rotational speed region and a possible reduction of turbo lag represent other benefits related to ETC application. On the other hand, the adoption of an ETC to a CI engine shows larger benefits in term energy recovery at the highest engine speeds, with consequent reduction of fuel consumption, mainly due to the absence of throttling effects in the intake manifold and related pumping losses.

Evaluation of an electric turbo compound system for SI engines: A numerical approach

by Stefano Frigo and Massimo Ceraolo

Applied Energy, 2016

Electric Turbo Compound (ETC) can improve exhaust gas energy recovery in Internal Combustion Engi... more Electric Turbo Compound (ETC) can improve exhaust gas energy recovery in Internal Combustion Engine (ICE). Models of a SI-ICE with ETC and whole vehicle were created using 1-D numerical codes. At ICE operating fixed point the ETC is not beneficial over a conventional turbocharger with appropriate turbine sizing. ETC can slightly improve overall efficiency when the ICE must provide variable power output. ETC application is more advantageous in motorway cycles, since the engine works at high loads and speeds.

Hydrogen generation system for ammonia–hydrogen fuelled internal combustion engines

International Journal of Hydrogen Energy, 2015

Ammonia cracking Catalytic reactor Spark-ignition engine Carbon free emissions a b s t r a c t Am... more Ammonia cracking Catalytic reactor Spark-ignition engine Carbon free emissions a b s t r a c t Ammonia is a well known hydrogen carrier which can be effectively utilized as a fuel in internal combustion engines (ICEs) when a small percentage of other fuels are added as combustion promoters. Among them, hydrogen is certainly the most valuable since it is carbon free and has opposed and complementary characteristics to those of ammonia.

Numerical Evaluation of an Electric Turbo Compound for SI Engines

by Paolo Bolognesi, Silvia Marelli, and Stefano Frigo

SAE Technical Paper Series, 2014

Experimental Study on ATAC (Active Thermo-Atmosphere Combustion) in a Two-Stroke Gasoline Engine

SAE Technical Paper Series, 1997

... Experimental Study on ATAC (Active Thermo-Atmosphere Combustion) in a Two-Stroke Gasoline Eng... more

Ammonia Plus Hydrogen as Fuel in a S.I. Engine: Experimental Results

by Stefano Frigo and N. Doveri

SAE Technical Paper Series, 2012

Diesel Fuel by Scrap-Tyre Thermal-Mechanical Pyrolysis

by Stefano Frigo, Maurizia Seggiani, and Monica Puccini

Implementation of a novel hydrogen direct-injection concept in single and multi-cylinder engines: CFD, experimental and engine powertrain design studies

International Journal of Powertrains, 2014

A novel low-pressure hydrogen direct-injection system, characterised by low storage residual pres... more A novel low-pressure hydrogen direct-injection system, characterised by low storage residual pressure and simple mechanical solutions, has been implemented in single and multi-cylinder engines. Based on two-step operation, this system keeps hydrogen metering apart from injection. The first step relates to the system with constant H 2 flow rate and variable opening duration. The second step is characterised by variable H 2 flow rate and constant angular duration. A prototype has been realised modifying a single-cylinder production engine, following the results of a wide CFD activity during which in-cylinder hydrogen injection and mixing phases have been simulated to investigate how valve and seat-valve geometries affect mixing characteristics. The prototype engine ran properly at full load, without pre-ignition, knocking or roughness even with stoichiometric or slightly rich mixtures, providing higher maximum power than with gasoline. At part load the engine worked correctly even with very lean mixtures. Current research is directed to explore the feasibility of applying the two-step injection concept in a multi-cylinder engine. The CFD analysis together with the design study aimed to integrate the injection system in the engine powertrain are shown and discussed.

Further Insight into the Possibility to Fuel a SI Engine with Ammonia plus Hydrogen

SAE Technical Paper Series, 2014

Behaviour of a Small Two-Stroke Engine with Direct Liquid Injection and Stratified Charge

SAE Technical Paper Series, 2004

High-pressure liquid fuel injection is a suitable means to get either stratified charge or homoge... more High-pressure liquid fuel injection is a suitable means to get either stratified charge or homogeneous charge for two-stroke engines. This paper shows the development of this solution for a small 50 cm 3 engine for light motorcycles. By means of computational fluid dynamics, a combustion chamber suitable for proper fuel distribution in every engine operating condition has been designed. It has been realized, and experimental results confirm its fairly satisfactory behaviour, with good fuel economy, low exhaust emissions and small cycle-to-cycle variation even at light loads. Recent CFD studies indicate how to improve engine geometry to achieve a better stratification stability at partial loads independently on engine speed.

Experimental Results Using Ammonia Plus Hydrogen in a S.I. Engine

by Stefano Frigo and Giacomo Ricci

Lecture Notes in Electrical Engineering, 2012

Simultaneous Reduction of Soot and NO X Emissions by Means of the HCPC Concept: Complying with the Heavy Duty EURO 6 Limits without Aftertreatment System

SAE Technical Paper Series, 2013

Due to concerns regarding pollutant and CO 2 emissions, advanced combustion modes that can simult... more Due to concerns regarding pollutant and CO 2 emissions, advanced combustion modes that can simultaneously reduce exhaust emissions and improve thermal efficiency have been widely investigated. The main characteristic of the new combustion strategies, such as HCCI and LTC, is that the formation of a homogenous mixture or a controllable stratified mixture is required prior to ignition. The major issue with these approaches is the lack of a direct method for the control of ignition timing and combustion rate, which can be only indirectly controlled using high EGR rates and/or lean mixtures.

Experimental Activity on a Hydrogen Fuelled S.I. Engine with Two-Step D.I

SAE Technical Paper Series, 2011

An innovative hydrogen DI system was conceived, realized and tested that requires only 12 bar rai... more An innovative hydrogen DI system was conceived, realized and tested that requires only 12 bar rail pressure, typical value of PFI systems, and does not need special injectors. The purpose is to combine the well known benefits of DI with the ones of PFI. The injection is accomplished in two steps: at first hydrogen, metered by an electroinjector (a conventional one for CNG application), enters a small intermediate chamber; then it is injected into the cylinder by means of a mechanically-actuated valve that allows very high flow rate (compared with the one of electroinjectors). In-cylinder injection starts at intake valve closing (an earlier injection start could lead to backfire) and stops early enough to allow proper charge homogeneity and, in any case, before cylinder pressure rise constrains hydrogen admission. The prototype engine was realised modifying a production single-cylinder 650 cm 3 engine with three intake valves. The central one was modified and properly timed to inject hydrogen into the cylinder from the intermediate chamber.

Two-Step Low-Pressure Direct Injection System for Hydrogen Fuelled Engines

SAE Technical Paper Series, 2010

A Hybrid Vehicle Powered by Hydrogen and Ammonia

by Giuseppe Pozzana, N. Doveri, Neri Bonfanti, Stefano Frigo, and Virgilio Mattoli

SAE Technical Paper Series, 2012

Development of a new steady state zero-dimensional simulation model for woody biomass gasification in a full scale plant

by Stefano Frigo and Roberto Gabbrielli

Energy Conversion and Management, 2016

A new steady state zero-dimensional simulation model for a full-scale woody biomass gasification ... more A new steady state zero-dimensional simulation model for a full-scale woody biomass gasification plant with fixed-bed downdraft gasifier has been developed using Aspen Plus Ò . The model includes the technical characteristics of all the components (gasifier, cyclone, exchangers, piping, etc.) of the plant and works in accordance with its actual main control logics. Simulation results accord with those obtained during an extensive experimental activity. After the model validation, the influence of operating parameters such as the equivalent ratio, the biomass moisture content and the gasifying air temperature on syngas composition have been analyzed in order to assess the operative behavior and the energy performance of the experimental plant. By recovering the sensible heat of the syngas at the outlet of the gasifier, it is possible to obtain higher values of the gasifying air temperature and an improvement of the overall gasification performances.

Electric Turbo Compounding Applied to a CI Engine: A Numerical Evaluation of Different Layouts

ASME 2016 Internal Combustion Engine Fall Technical Conference, 2016

At present, the application of turbocharging in compression ignition (CI) engines represents almo... more At present, the application of turbocharging in compression ignition (CI) engines represents almost all of the applications, especially for transportation where fuel efficiency and low emissions are the main targets. Following this approach, the possibility to couple an electric drive to the turbocharger (electric turbo compound, ETC) to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world.

Mathematical modelling and energy performance assessment of air impingement drying systems for the production of tissue paper

by Stefano Frigo and Roberto Gabbrielli

Energy, 2016

In this paper an original and exhaustive mathematical modelling of air impingement drying systems... more In this paper an original and exhaustive mathematical modelling of air impingement drying systems for the production of tissue paper in the Yankee-hoods configurations is reported, which offers the possibility to optimize its energy performance. The model takes into account many detailed operative parameters of the overall drying process with the aim to execute its energy and mass balance and to evaluate its energy performances. The validity of the mathematical model has been assessed by comparison with actual data from an existing tissue paper mill. Finally, the energy performances of two different layouts of the air system have been evaluated and compared. Changing the operative parameters of the drying process, such as air jet temperature and speed and moisture content of the extraction air, it is possible to obtain the same paper production with an energy saving of about 4.5%. In average, the layout with two parallel air circuits assure an energy saving of about 1% with respect to the layout with a single air circuit.

Development of a pumpless air-assisted injection system for two-cycle, S.I. engines

Sae Transactions, 1994

Further insight on ATAC and GDI combination in two-stroke engines

Sae Transactions, 2000

In two-stroke S.I. engines, direct fuel injection prevents fuel loss from the exhaust port, since... more In two-stroke S.I. engines, direct fuel injection prevents fuel loss from the exhaust port, since only air is employed for the scavenging process. However, to solve the problem of combustion irregularity at light loads due to excessive presence of residual gas in the charge, fuel injection should also produce charge stratification.

Numerical Comparison of an Electric Turbo Compound Applied to a SI and a CI Engine

Volume 2: Emissions Control Systems; Instrumentation, Controls, and Hybrids; Numerical Simulation; Engine Design and Mechanical Development, 2015

In a medium term scenario Internal Combustion Engine (ICE) downsizing and hybrid powertrain will ... more In a medium term scenario Internal Combustion Engine (ICE) downsizing and hybrid powertrain will represent the actual trend in vehicle technology to reduce fuel consumption and CO 2 emission. Concerning downsizing concept, to maintain a reasonable power level in small engines, the application of turbocharging is mandatory both for spark ignition (SI) and compression ignition (CI) engines. Following this aspect, the possibility to couple an electric machine to the turbocharger (electric turbo compound, ETC) to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world and by the current application in the F1 Championship. The present paper shows the first numerical results of a research program focused on the comparison of the benefits resulting from the application of an ETC to a small twincylinder SI engine (900 cm 3 ) and to a four cylinders CI engine (1600 cm 3 ), both of the same maximum power. Starting from the experimental maps of several turbines and compressors, complete model of both turbocharged engines were created using the AVL BOOST one-dimension code. Concerning the SI engine, first numerical results show that ETC can improve the average overall efficiency at the highest engine speeds and loads. Besides, boost range extension in the lowest engine rotational speed region and a possible reduction of turbo lag represent other benefits related to ETC application. On the other hand, the adoption of an ETC to a CI engine shows larger benefits in term energy recovery at the highest engine speeds, with consequent reduction of fuel consumption, mainly due to the absence of throttling effects in the intake manifold and related pumping losses.

Evaluation of an electric turbo compound system for SI engines: A numerical approach

by Stefano Frigo and Massimo Ceraolo

Applied Energy, 2016

Electric Turbo Compound (ETC) can improve exhaust gas energy recovery in Internal Combustion Engi... more Electric Turbo Compound (ETC) can improve exhaust gas energy recovery in Internal Combustion Engine (ICE). Models of a SI-ICE with ETC and whole vehicle were created using 1-D numerical codes. At ICE operating fixed point the ETC is not beneficial over a conventional turbocharger with appropriate turbine sizing. ETC can slightly improve overall efficiency when the ICE must provide variable power output. ETC application is more advantageous in motorway cycles, since the engine works at high loads and speeds.

Hydrogen generation system for ammonia–hydrogen fuelled internal combustion engines

International Journal of Hydrogen Energy, 2015

Ammonia cracking Catalytic reactor Spark-ignition engine Carbon free emissions a b s t r a c t Am... more Ammonia cracking Catalytic reactor Spark-ignition engine Carbon free emissions a b s t r a c t Ammonia is a well known hydrogen carrier which can be effectively utilized as a fuel in internal combustion engines (ICEs) when a small percentage of other fuels are added as combustion promoters. Among them, hydrogen is certainly the most valuable since it is carbon free and has opposed and complementary characteristics to those of ammonia.

Numerical Evaluation of an Electric Turbo Compound for SI Engines

by Paolo Bolognesi, Silvia Marelli, and Stefano Frigo

SAE Technical Paper Series, 2014

Experimental Study on ATAC (Active Thermo-Atmosphere Combustion) in a Two-Stroke Gasoline Engine

SAE Technical Paper Series, 1997

... Experimental Study on ATAC (Active Thermo-Atmosphere Combustion) in a Two-Stroke Gasoline Eng... more

Ammonia Plus Hydrogen as Fuel in a S.I. Engine: Experimental Results

by Stefano Frigo and N. Doveri

SAE Technical Paper Series, 2012

Diesel Fuel by Scrap-Tyre Thermal-Mechanical Pyrolysis

by Stefano Frigo, Maurizia Seggiani, and Monica Puccini

Implementation of a novel hydrogen direct-injection concept in single and multi-cylinder engines: CFD, experimental and engine powertrain design studies

International Journal of Powertrains, 2014

A novel low-pressure hydrogen direct-injection system, characterised by low storage residual pres... more A novel low-pressure hydrogen direct-injection system, characterised by low storage residual pressure and simple mechanical solutions, has been implemented in single and multi-cylinder engines. Based on two-step operation, this system keeps hydrogen metering apart from injection. The first step relates to the system with constant H 2 flow rate and variable opening duration. The second step is characterised by variable H 2 flow rate and constant angular duration. A prototype has been realised modifying a single-cylinder production engine, following the results of a wide CFD activity during which in-cylinder hydrogen injection and mixing phases have been simulated to investigate how valve and seat-valve geometries affect mixing characteristics. The prototype engine ran properly at full load, without pre-ignition, knocking or roughness even with stoichiometric or slightly rich mixtures, providing higher maximum power than with gasoline. At part load the engine worked correctly even with very lean mixtures. Current research is directed to explore the feasibility of applying the two-step injection concept in a multi-cylinder engine. The CFD analysis together with the design study aimed to integrate the injection system in the engine powertrain are shown and discussed.

Further Insight into the Possibility to Fuel a SI Engine with Ammonia plus Hydrogen

SAE Technical Paper Series, 2014

Behaviour of a Small Two-Stroke Engine with Direct Liquid Injection and Stratified Charge

SAE Technical Paper Series, 2004

High-pressure liquid fuel injection is a suitable means to get either stratified charge or homoge... more High-pressure liquid fuel injection is a suitable means to get either stratified charge or homogeneous charge for two-stroke engines. This paper shows the development of this solution for a small 50 cm 3 engine for light motorcycles. By means of computational fluid dynamics, a combustion chamber suitable for proper fuel distribution in every engine operating condition has been designed. It has been realized, and experimental results confirm its fairly satisfactory behaviour, with good fuel economy, low exhaust emissions and small cycle-to-cycle variation even at light loads. Recent CFD studies indicate how to improve engine geometry to achieve a better stratification stability at partial loads independently on engine speed.

Experimental Results Using Ammonia Plus Hydrogen in a S.I. Engine

by Stefano Frigo and Giacomo Ricci

Lecture Notes in Electrical Engineering, 2012

Simultaneous Reduction of Soot and NO X Emissions by Means of the HCPC Concept: Complying with the Heavy Duty EURO 6 Limits without Aftertreatment System

SAE Technical Paper Series, 2013

Due to concerns regarding pollutant and CO 2 emissions, advanced combustion modes that can simult... more Due to concerns regarding pollutant and CO 2 emissions, advanced combustion modes that can simultaneously reduce exhaust emissions and improve thermal efficiency have been widely investigated. The main characteristic of the new combustion strategies, such as HCCI and LTC, is that the formation of a homogenous mixture or a controllable stratified mixture is required prior to ignition. The major issue with these approaches is the lack of a direct method for the control of ignition timing and combustion rate, which can be only indirectly controlled using high EGR rates and/or lean mixtures.

Experimental Activity on a Hydrogen Fuelled S.I. Engine with Two-Step D.I

SAE Technical Paper Series, 2011

An innovative hydrogen DI system was conceived, realized and tested that requires only 12 bar rai... more An innovative hydrogen DI system was conceived, realized and tested that requires only 12 bar rail pressure, typical value of PFI systems, and does not need special injectors. The purpose is to combine the well known benefits of DI with the ones of PFI. The injection is accomplished in two steps: at first hydrogen, metered by an electroinjector (a conventional one for CNG application), enters a small intermediate chamber; then it is injected into the cylinder by means of a mechanically-actuated valve that allows very high flow rate (compared with the one of electroinjectors). In-cylinder injection starts at intake valve closing (an earlier injection start could lead to backfire) and stops early enough to allow proper charge homogeneity and, in any case, before cylinder pressure rise constrains hydrogen admission. The prototype engine was realised modifying a production single-cylinder 650 cm 3 engine with three intake valves. The central one was modified and properly timed to inject hydrogen into the cylinder from the intermediate chamber.

Two-Step Low-Pressure Direct Injection System for Hydrogen Fuelled Engines

SAE Technical Paper Series, 2010

A Hybrid Vehicle Powered by Hydrogen and Ammonia

by Giuseppe Pozzana, N. Doveri, Neri Bonfanti, Stefano Frigo, and Virgilio Mattoli

SAE Technical Paper Series, 2012