Stefano Frigo

Small-scale wood-fuelled CHP plants: A comparative evaluation of the available technologies

Actually, several applications of small (≤1 MWe) CHP (Combined Heat and Power) plants fuelled with solid wood can be found in Europe. Innovative technologies are facing the market, giving new perspectives for wood utilisation in district heating and/or in industrial-commercial activities. However, while the energy saving and the environmental benefits of CHP plants are undoubted, technological and no technological barriers still obstacle their large diffusion. The present study reports a comparative evaluation of the different available technologies in terms of thermal and electric efficiencies and their possible applications. Taking into consideration the electricthermal performances of each configuration and the actual economic incentives guaranteed by the Italian government, a preliminary estimation of economic convenience of each plant is given.

Two-Step Concept for Low-Pressure Direct Hydrogen Injection

In this paper, a low-pressure hydrogen direct-injection solution is presented that entails low storage residual pressure (∼12 bar). The injection is realised in two steps. First, hydrogen is simply metered by an electro-injector (a conventional one for Compressed Natural Gas - CNG application) that feeds a small intermediate chamber. Next, hydrogen enters the cylinder by means of a mechanically-actuated valve which allows higher flow than any electro-injector. Injection must end early enough to allow good charge homogeneity and, in any case, before in-cylinder pressure rise constraints hydrogen admission. Backfire is avoided by starting injection at intake valve closing. A prototype has been realised modifying a single-cylinder 650 cc production engine with three intake valves. The central one has been modified and properly timed to in-cylinder inject hydrogen from the intermediate chamber. Hydrogen injection through different-shape poppet valves in a quiescent, constant volume has been simulated in order to investigate the effects of valve and seat-valve geometries in controlling fuel-air mixing in the cylinder. Additional predictions for the actual engine configuration indicate that an acceptable fuel distribution can be obtained in the combustion chamber at the spark timing, with equivalence ratios in the ignition region that are inside the flammability range of the mixture for all the operating conditions (loads and speeds) that have been considered.© 2009 ASME

Direct Injection and Charge Stratification in a 50 cc Two-Stroke Engine: CFD Studies and Test Bench Results

Direct fuel injection has become necessary in two-stroke S.I. engines, since it prevents one of the major problems of these engines, that is fuel loss from the exhaust port. Another important problem is combustion irregularity at light loads, due to excessive residual gas in the charge, and can be solved by charge stratification. High-pressure liquid fuel injection is able to control the mixing process inside the cylinder for getting either stratified charge at partial loads or quasi-stoichiometric conditions, as it is required at full load. The feasibility of this solution for a small engine for light motorcycles has been studied using CFD tools. An exhaustive investigation carried out by the KIVA3v code allowed to design a 50 cm3 engine prototype with a satisfactory behaviour even at light loads in unthrottled condition, as proved by good fuel economy and engine stability in dynamometric bench tests. Exhaust gas analysis and indicated pressure behaviour confirm stratification and combustion correctness. For the final part of the research the adoption of the AVL-Fire code has been considered: the possibility to take into account any combustion chamber and transfer duct geometric details and the accuracy of spray breakup and wall film models allow to better understand the engine behaviour throughout the operating range, obtaining useful information in order to efficiently shorten the experimental time required for the EU map-setting.© 2006 ASME

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

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 CO2 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 twin-cylinder SI engine (900 cm3) and to a four cylinders CI engine (1600 cm3), 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.Copyright

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

In the prospective to reduce greenhouse gas emission from vehicles, the use of hydrogen as fuel represents a possible solution. However, if proper engine running with hydrogen has been widely demonstrated, hydrogen storage onboard of the vehicle is a major problem. A promising solution is storing hydrogen in the form of ammonia that is liquid at roughly 9 bar at environmental temperature and therefore involves relatively small volumes and requires light and low-cost tanks. Moreover, liquid ammonia contains 1.7 times by volume as much hydrogen as liquid hydrogen itself. It is well known that ammonia can be burned directly in I.C. engines, however a combustion promoter is necessary to support combustion especially in the case of high-speed S.I. engines. As a matter of fact, the best (and carbon-free!) promoter is hydrogen, which has very high combustion velocity and wide flammability range, whereas ammonia combustion is characterised by low flame speed, low flame temperature, narrow flammability range (combustion is impossible if mixture is just slightly lean), high ignition energy and high self-ignition temperature. The experimental activity shown in the paper was aimed at determining proper air-ammonia-hydrogen mixture compositions for the actual operating conditions of a twin-cylinder 505 cm3 S.I. engine. Hydrogen and ammonia are separately injected in the gaseous phase. The experimental results confirm that it is necessary to add hydrogen to air-ammonia mixture to improve ignition and to speed up combustion, with ratios that depend mainly on load and less on engine speed. This activity is correlated with a larger-scale project, founded by Tuscany Region, in which a partnership of research and industry entities has developed a fully-working plug-in hybrid electric vehicle equipped with a range-extending 15 kW IC engine fuelled with hydrogen and ammonia. Hydrogen is obtained from ammonia by means of on-board catalytic reforming.

Validation of a Small Scale Woody Biomass Downdraft Gasification Plant Coupled with Gas Engine

Validation of a Small Scale Woody Biomass Downdraft Gasification Plant Coupled with Gas Engine Roberto Gabbrielli*, Maurizia Seggiani, Stefano Frigo, Monica Puccini, Sandra Vitolo, Giovanni Raggio, Fulvio Puccioni a Department of Civil and Industrial Engineering, University of Pisa, Largo Lucio Lazzarino 1, 56122 Pisa, Italy. b Department of Energy, System, Territory and Construction Engineering, University of Pisa, Largo Lucio Lazzarino 1, 56122 Pisa, Italy. C Glass Service s.r.l , Via Cascina Lari , 56028 San Miniato, Italy. r.gabbrielli@ing.unipi.it

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

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 H2 flow rate and variable opening duration. The second step is characterised by variable H2 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.

Numerical and Experimental Analysis on a Small GDI, Stratified Charge, Motorcycle Engine

In the field of engines for light motorcycles, two-stroke cycle survival is submitted to the application of direct fuel injection and charge stratification, even in the case of low-cost small engines. However, charge stratification is a difficult target in two-stroke engines, chiefly because timings of late injection (necessary for charge stratification) and of early injection (necessary for homogeneous charge) are much closer than in four-stroke engines. The compatibility between stratified and homogeneous charge operations needs a thorough CFD study of injection and mixing processes, with the support of techniques of spray visualization. Results strongly depend on the possibility of optimising the interaction between in-cylinder gas-dynamic field and spray; experimental activity is necessary as data source and verification of computational prediction. This paper shows the latest CFD investigation, experimental tests and results concerning a 50 cm3 engine for light motorcycles. The injection is of the liquid type with wall-and-air guided spray produced by a swirl injector. The research has been focused on the attainment of charge stratification at every engine speed. Spray actual characteristics have been investigated, attesting suitable repeatability and proper variation versus backpressure. Engine satisfactory behaviour even at light loads in unthrottled condition is proved by good fuel economy and engine stability in dynamometric bench tests. Exhaust gas analysis and indicated pressure behaviour confirm stratification and combustion correctness.Copyright