COMBUSTION HEAT RELEASE RATE CALCULATIONS

Transcription

1 computation of Net Heat Releae Rate analyi i the combution preure crank angle hitory in the combution chamber. COMBUSION HEA RELEASE RAE CALCULAIONS

2 CHAPER-III HEA RELEASE RAE CACULAIONS Preure crank angle hitory i obtained from the engine data logger for the defined engine load. After obtaining data from the combution cycle, net heat releae rate i calculated baed on the firt law of thermodynamic. Heat tranfer from the gae to cylinder i computed, and deducted from the gro heat releae rate to arrive at net heat releae rate and preented in the form of graph. he computed Heat Releae Rate (NHRR and CHRR) profile are hown in figure 3. and 3.3, for the recorded preure data of the engine cylinder in figure 3.1. When analyzing internal combution engine, the in-cylinder preure ha alway been an important experimental diagnotic due to it direct relation to the combution and work producing procee. he in-cylinder preure reflect the combution proce involving piton work produced by the ga (due to change in cylinder volume), heat tranfer to the combution chamber wall a well a ma flow in and out of crevice region between the piton, piton ring and cylinder liner. hu, for accurate reult it i required to know how the combution proce propagate through combution chamber and each of thee procee mut be related to cylinder preure Richard tone [1999], Heywood [1988], o the combution proce can be ditinguihed. Reduction of an effective change in volume, heat tranfer and ma lo at the cylinder preure i called heat releae analyi and i done within the framework of the firt law of thermodynamic, when the intake and exhaut valve are cloed, i.e. during the cloed part of engine cycle. he implet approach i to conider cylinder content a a ingle zone, whoe thermodynamic tate and propertie are modeled, being uniform throughout the cylinder and repreented by the average value. A no patial variation are conidered, o the model i aid to be zero-dimenional. Model for the heat tranfer and crevice effect can be eaily included to analyze. Krieger R. B., Borman have contributed a lot to develop the Heat releae rate model for the I C engine. 3.1 Heat releae baed on I t Law of thermodynamic On the bai of firt law of thermodynamic the heat releae model i:

3 dq n dv 1 dp C p p V d 1 d 1, where, R C p Cv d C he ga temperature can be found from the equation of tate ( pv mr ), ince the preure and volume are known, and it ha been aumed ma i contant. he ga propertie vary with temperature, but the variation i modet, it i acceptable in mot cae to evaluate the propertie at the ga temperature computed in the previou increment. Equation below can be ued to evaluate the propertie u and R, from which can be evaluated. Once the ga temperature ha been evaluated, it i poible to etimate the rate of heat tranfer, by auming wall temperature and employing a heat tranfer correlation. An approach adopted by Krieger and Borman [1966] i ued in thi work. hey provided polynomial coefficient from the curve fit to combution problem calculation for weak mixture ( 1) of CnH n with air. u K ) K kj/ kgof original air, Where K 1= 1( v K With ga contant given by: R kj/ kgof original air / K 3. In cylinder heat tranfer hi model incorporate all the procee taking place in the cylinder for heat tranfer calculation, i.e. in-cylinder air motion, fuel pray development and mixing, pray impingement on the wall, turbulence, droplet evaporation, fuel ignition delay and combution proce. inananeou bulk gatemperature(k), mean urface temperature(k ) A inananeou urfacearea ( m ), Q Inananeou heat flow rate(w ) Annand and Ma [1971] have developed the following equation for heat tranfer: Q A k c B Re b ( ) d( ) k=thermal conductivity, B=Bore diameter, k 0.75

4 And for a compreion ignition engine Waton and Janota 198 uggeted that b 0.7, 0.5 c 0. 8, d 0.576, where = Stefan- Boltzmann contant he obtained graph for the net heat releae and cumulative heat releae rate have been enviaged in figure 3. and 3.3. he value have been calculated from the real time combution preure logged by Preure - crank angle data logger uing excel chart. Fig.3.1 Input preure data ignature drawn at different load in limited range of 0 0 to 70 0 crank angle with 90% BD(COME) + 10% riacetin blend fuel run

5 Fig.3. Net heat releae rate at different load in limited range of 30 0 to 10 0 crank angle with 90% BD(COME) + 10% riacetin blend fuel Fig.3.3 Cumulative heat releae rate at different load in limited range from to 30 0 crank angle with 90% BD(COME) + 10% riacetin blend fuel 3.3 Summary he computed Heat Releae Rate (NHRR and CHRR) profile are drawn for the recorded preure data of the engine cylinder with repect to crank angle. he other graph drawn are hown in reult and appendix for the experiment conducted with dieel, biodieel and triacetin additive -COME blend a fuel. he following chapter (Chapter-IV) deal with experimental et up and experimentation. A laboratory baed direct injection dieel engine i ued to tet triacetin additive - COME biodieel blend at variou percentage by volume.