2,723 research outputs found
A New Simple Function for Combustion and Cyclic Variation Modeling in Supercharged Spark Ignition Engines
No full textResearch in the field of Internal Combustion (IC) engines focuses on the drastic reduction of both pollutant and greenhouse gas emissions. A promising alternative to gasoline and diesel fuel is represented by the use of gaseous fuels, above all green hydrogen but also Natural Gas (NG). In previous works, the authors investigated the performance, efficiency, and emissions of a supercharged Spark Ignition (SI) engine fueled with mixtures of gasoline and natural gas; a detailed research involving the combustion process of this kind of fuel mixture has been previously performed and a lot of experimental data have been collected. Combustion modeling is a fundamental tool in the design and optimization process of an IC engine. A simple way to simulate the combustion evolution is to implement a mathematical function that reproduces the mass fraction burned (MFB) profile; the most used for this purpose is the Wiebe function. In a previous work, the authors proposed an innovative mathematical model, the Hill function, that allowed a better interpolation of experimental MFB profiles when compared to the Wiebe function. In the research work presented here, both the traditional Wiebe and the innovative Hill function have been calibrated using experimental MFB profiles obtained from a supercharged SI engine fueled with mixtures of gasoline and natural gas in different proportions; the two calibrated functions have been implemented in a zero-dimensional (0-D) SI engine model and compared in terms of both Indicated Mean Effective Pressure (IMEP) and cyclic pressure variation prediction reliability. It was found that the Hill function allows a better IMEP prediction for all the operating conditions tested (several engine speeds, supercharging pressures, and fuel mixtures), with a maximum prediction error of 2.7% compared to 4.3% of the Wiebe function. A further analysis was also performed regarding the cyclic pressure variation that affects all the IC engines during combustion and may lead to irregular engine operation; in this case, the Hill function proved to better predict the cyclic pressure variation with respect to the Wiebe function
On the Use of a Hydrogen-Fueled Engine in a Hybrid Electric Vehicle
No full textHybrid electric vehicles are currently one of the most effective ways to increase the efficiency and reduce the pollutant emissions of internal combustion engines. Green hydrogen, produced with renewable energies, is an excellent alternative to fossil fuels in order to drastically reduce engine pollutant emissions. In this work, the author proposes the implementation of a hydrogen-fueled engine in a hybrid vehicle; the investigated hybrid powertrain is the power-split type in which the engine, two electric motor/generators and the drive shaft are coupled together by a planetary gear set; this arrangement allows the engine to operate independently from the wheels and, thus, to exploit the best efficiency operating points. A set of numeric simulations were performed in order to compare the gasoline-fueled engine with the hydrogen-fueled one in terms of the thermal efficiency and total energy consumed during a driving cycle. The simulation results show a mean engine efficiency increase of around 17% when fueled with hydrogen with respect to gasoline and an energy consumption reduction of around 15% in a driving cycle
An Effective Method to Model the Combustion Process in Spark Ignition Engines
No full textA numerical simulation is a fundamental tool in the design and optimization procedure of an Internal
Combustion (IC) engine; since combustion is the process that mostly influences the engine performance,
efficiency and emissions, an effective combustion submodel is fundamental. A simple,
nonpredictive way to simulate the combustion evolution is to implement a mathematical function
that reproduces the mass fraction burned (MFB) profile that is characterized by a sigmoidal trend;
the most used for this purpose is the Wiebe function. In this article the authors propose a different
mathematical model, a Dose-Response (DR) type function that shows some benefits when compared
to the Wiebe function, in particular, a better interpolation of experimental MFB profiles in which the
combustion extinction phase represents a large fraction of the whole combustion duration; this
happens, for example, in Spark Ignition (SI) engines with a noncentral location of the spark plug,
which produces an asymmetric combustion propagation and, in turn, an asymmetric derivative of
the experimental MFB profile. In this article both the traditional Wiebe and the proposed DR function
have been calibrated by means of experimental MFB profiles obtained from a supercharged SI engine
fueled with natural gas; the two calibrated functions have been implemented in a zero-dimensional
(0-D) SI engine model and compared in terms of Indicated Mean Effective Pressure (IMEP) prediction
reliability. The proposed DR function allowed both a better MFB profile interpolation and a
better IMEP prediction for all the operating conditions tested (different engine speed and supercharging
pressure), with a maximum prediction error of 2.1% compared with 2.9% of the Wiebe function
A Comprehensive Model for the Auto-Ignition Prediction in Spark Ignition Engines Fueled With Mixtures of Gasoline and Methane-Based Fuel
No full textThe 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 mixtures or gasoline-methane mixtures. The model takes into account the negative temperature coefficient (NTC) behavior of fuels and has been calibrated using a considerable amount of knocking in-cylinder pressure cycles acquired on a Cooperative Fuel Research (CFR) engine widely varying compression ratio (CR), inlet temperature, spark advance (SA), and fuel mixture composition, thus giving the model a general validity for the simulation of naturally aspirated or supercharged engines. As a result, the auto-ignition onset is predicted with maximum and mean error of 4.5 and 1.4 crank angle degrees (CAD), respectively, which is a negligible quantity from an engine control standpoint
Reliable TDC position determination: a comparison of different thermodynamic methods through experimental data and simulations
No full textIt 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 pressure (IMEP) and a 25% error on the heat released by the combustion: the TDC position should be then known within a precision of 0.1 CAD. This task can be accomplished by means of a dedicated capacitive sensor, which allows a measurement within the required 0.1 degrees precision. Such a sensor has a substantial cost and its use is not really fast; a different approach can be followed using a thermodynamic method, whose input is the pressure curve sampled during the compression and expansion strokes of a “motored” (i.e. without combustion) cylinder.In this work the authors compare an original thermodynamic method with other ones available in literature, by means of both experimental and simulated pressure curves. A zero dimensional thermodynamic model was employed to obtain an extensive collection of numeric pressure curves by changing engine geometry (e.g. compression ratios from 10 to 20 were adopted), operative conditions and wall heat transfer laws. The in-cylinder mass leakage has been taken into account in the model.Moreover, in order to assess the reliability and robustness of each method, the typical measurement errors and disturbances related to indicating analysis have been taken into account. The capability of the investigated methods to provide the correct TDC position in presence of the above mentioned errors has been evaluated
The Experimental Validation of a New Thermodynamic Method for TDC Determination
No full textIn-cylinder pressure analysis is becoming more and more important both for research and development purpose and for control and diagnosis of internal combustion engines; directly measured by means of combustion chamber transducers or evaluated by means of engine speed analysis, in-cylinder pressure allows the evaluation of indicated mean effective pressure (IMEP), combustion heat release, combustion phase, friction pressure, etc...It is well known to internal combustion engine researchers that for a right evaluation of these quantities the exact determination of Top Dead Centre (TDC) is of vital importance: a 1° error on TDC determination can leads to evaluation errors of about 10% on the IMEP and 25% on the heat released by the combustion. In this paper the authors present the experimental validation of an original thermodynamic method for the correct evaluation of the “loss angle”, i.e. the angular phase shift between the TDC location and the pressure peak location. The validation has been carried out on a spark ignition engine comparing the results of the thermodynamic method, whose input is the in-cylinder pressure acquired in a “motored” cylinder (i.e. without combustion), with those obtained from a commercial available TDC sensor. The comparative tests aimed to characterize the precision of the proposed method
Confronto sperimentale tra metodi termodinamici per la determinazione della posizione del punto morto superiore
No full text“Determinazione analitica della fasatura ottima di combustione in motori ad accensione comandata” 63° Congresso Nazionale ATI, Palermo Sett. 2008
No full textAn analytical approach for the evaluation of the optimal combustion phase in spark ignition engines
No full textIt is well known that the spark advance is one of the most important parameters influencing the efficiency of a S.I. engine. A change in this parameter causes a shift in the combustion phase, whose optimal position, with respect to the piston motion, implies the maximum brake mean
effective pressure (bmep), for given operative conditions. The best spark timing is usually estimated by means of experimental trials on the engine test bed or by means of thermodynamic simulations
of the engine cycle. In this work, instead, the authors developed, under some simplifying
hypothesis, an original theoretical formulation for the estimation of the optimal combustion phase.
The most significant parameters involved with the combustion phase are taken into consideration;
in particular, the influence of the combustion duration, of the heat release law, of the heat transfer to the combustion chamber walls and of the mechanical friction losses are evaluated.
The theoretical conclusion, experimentally proven by many authors, is that the central point of the combustion phase (known as the location of the 50% of mass fraction burnt, here called MFB50)must be delayed with respect to the TDC as a consequence of both heat exchange between gas and chamber walls and friction losses
Analysis of the Combustion Process in a Hydrogen-Fueled CFR Engine
No full textGreen hydrogen, produced using renewable energy, is nowadays one of the most promising alternatives to fossil fuels for reducing pollutant emissions and in turn global warming. In particular, the use of hydrogen as fuel for internal combustion engines has been widely analyzed over the past few years. In this paper, the authors show the results of some experimental tests performed on a hydrogen-fueled CFR (Cooperative Fuel Research) engine, with particular reference to the combustion. Both the air/fuel (A/F) ratio and the engine compression ratio (CR) were varied in order to evaluate the influence of the two parameters on the combustion process. The combustion duration was divided in two parts: the flame front development (characterized by laminar flame speed) and the rapid combustion phase (characterized by turbulent flame speed). The results of the hydrogen-fueled engine have been compared with results obtained with gasoline in a reference operating condition. The increase in engine CR reduces the combustion duration whereas the opposite effect is observed with an increase in the A/F ratio. It is interesting to observe how the two parameters, CR and A/F ratio, have a different influence on the laminar and turbulent combustion phases. The influence of both A/F ratio and engine CR on heat transfer to the combustion chamber wall was also evaluated and compared with the gasoline operation. The heat transfer resulting from hydrogen combustion was found to be higher than the heat transfer resulting from gasoline combustion, and this is probably due to the different quenching distance of the two fuels
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