alt="images"/> 283 K and Solution
The input parameters to the MATLAB® program CIHeatRelease.m are listed in the printout below.
Compression Ignition heat release Ti = 283; inlet temperature (K) Pi = 1.00; inlet pressure (bar) MWair = 28.97; air molecular mass (kg/kmol air) rc = 15; compression ratio S = 0.165; stroke (m) B = 0.165; bore (m) N = 1500; engine speed (rpm) PHI = 0.7; equivalence ratio F = 0.05; residual fraction FS = 0.06993; stoichiometric fuel‐‐air ratio ao = 45730; fuel available energy (kJ/kg) CN = 40; Cetane number THETAI = -12; start of injection (deg) THETAD = 15; injection duration (deg) ...
The
The mass of air in the cylinder at bdc is
The molar mass of air in the cylinder at bdc is
The injected fuel total energy
For an ignition delay
The energy release during the premixed phase is
and the energy release during the diffusion burn phase is
The diffusion energy release per kmol of air (MJ/
and the diffusion burn duration
The energy release profile produced by CIHeatRelease.m for the above engine parameters is plotted in Figure 2.24. The maximum energy release rate is during the premixed burn with a rate of about 750 J/deg at
Comment: One limitation of the dual Wiebe function approach for compression ignition is that it is difficult to represent multiple pilot and post fuel injections. For each additional injection, an additional Wiebe function, with specific experimentally determined parameters, is required.
Diesel energy release profile for Example 2.7.
2.9 References
1 Ghojel, J. (2010), “Review of the Development and Applications of the Wiebe Function,” Int. J. Eng. Res., Vol. 11, pp. 297–312.
2 Foster, D. (1985) “An Overview of Zero‐Dimensional Thermodynamic Models for IC Engine Data Analysis,” SAE Technical Paper 852070.
3 Heywood, J. B. (2018), Internal Combustion Engine Fundamentals, McGraw‐Hill, New York.
4 Miller, R. H. (1947), “Supercharging and Internal Cooling Cycle for High Output,” ASME Transactions, Vol. 69, pp. 453–464.
5 Miyamoto, N., T. Chikahisa, T. Murayama, and R. Sawyer (1985), “Description and Analysis of Diesel Engine Rate of Combustion and Performance Using Wiebe's Functions,” SAE Technical Paper 850107.
6 Takita, Y., S. Kono, and A. Naoi (2011), “Study of Methods to Enhance Energy Utilization Efficiency of Micro Combined Heat and Power Units,” SAE Technical Paper 2011‐32‐0574.
2.10 Homework
1 2.1 The compression ratio of an ideal gas Otto cycle is . At the beginning of compression the pressure is 100 kPa and temperature is 300 K. The bore and stroke are both 0.085 m, and engine speed is 2000 rpm. The energy input to the working fluid is = 800 kJ/. Determine the temperature and pressure at each point in the cycle, the indicated work , the thermal efficiency , the indicated power , and the imep.
2 2.2 A throttled single cylinder spark‐ignition engine contains kg of fuel with a heat of combustion, , of 45,000 kJ/kg. The volume at top dead center of the cylinder is , and the volume at bottom dead center is . The air–fuel ratio is 16:1, and the mixture temperature at the start of compression is 300 K. The engine speed is 1500 rpm. Modeling the compression and combustion as an ideal gas ( kJ/kg‐K) Otto cycle, (a) What is the pressure at the start of compression? (b) what is the maximum temperature and pressure ? (c) What is the thermal efficiency and the indicated power ?
3 2.3 An engine is to be modeled with an Otto gas cycle. The engine has a compression ratio , inlet temperature = 298 K, and inlet pressure = 75 kPa. The air–fuel ratio AF = 15:1, the heat of combustion of the fuel is 47,900 kJ/kg, the gas constant of the fuel–air mixture is 0.29 kJ/kg‐K, and = 1.26. Using an ideal gas cycle model, what is the engine's maximum temperature and pressure, thermal efficiency, and imep?
4 2.4 The Lenoir air cycle is composed of three processes: 1‐2 constant volume heat addition, 2‐3 isentropic expansion, and 3‐1 constant pressure
