110 research outputs found
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
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
A Study on the Use of Combustion Phase Indicators for MBT Spark Timing on a Bi-Fuel Engine
No full textThe performance of a spark ignition engine strongly depends on the phase of the combustion process with respect to piston motion, and hence on the spark advance; this fundamental parameter is actually controlled in open-loop by means of maps drawn up on the test bench and stored in the Electronic Control Unit (ECU). Bi-fuel engines (e.g. running either on gasoline or on natural gas) require a double mapping process in order to obtain a spark timing map for each of the fuels. This map based open-loop control however does not assure to run the engine always with the best spark timing, which can be influenced by many factors, like ambient condition of pressure, temperature and humidity, fuel properties, engine wear. A feedback control instead can maintain the spark advance at its optimal value apart from operative and boundary conditions, so as to gain the best performance (or minimum fuel consumption). Such a control can be realized using as pilot variable a combustion phase indicator, i.e. a parameter which depends exclusively on the phase of the heat release process and assumes a fixed value for optimal spark timing. The purpose of the present work is to compare the behaviour of the most used combustion phase indicators using two different fuels one after the other (common gasoline and Compressed Natural Gas, CNG) on the same engine, in order to assess the influence of different heat release progress and to verify the possibility to feedback control the spark timing apart from the fuel used. The comparison has been carried on by means of experimental test on the engine test bench, analysing in-cylinder pressure acquired with varying spark advance for different operative conditions of engine speed, load and air-to-fuel ratio
Regolazione in retroazione dell’anticipo d’accensione mediante analisi della pressione all’interno del cilindro
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