Tutorials Manual

More documents

Recommendations

Info

Chemkin 4.1.1 Chapter 2: Combustion in Gas-phase Processes For this problem, we have some data from a single-cylinder HCCI test engine and would like to use the single-zone IC engine model to simulate the same HCCI process. We would also like to find out how sensitive the solutions are to the heat loss at cylinder wall. The HCCI engine for this problem runs on natural gas, a mixture of CH 4 , C 2 H 6 and C 3 H 8 , with exhaust gas recirculation (EGR). The use of EGR can provide some ignition control and CO 2 from the exhaust gas can keep combustion temperature low due to its relatively large heat capacity. Specifications of the test engine that are related to our model setup are given in Table 2-7. Table 2-7 Test Engine Specifications Parameter Setting Compression ratio 16.5 Cylinder clearance volume 103.3 cm 3 Engine speed 1000 rpm Connecting rod to crank radius ratio 3.714286 Cylinder bore diameter 12.065 cm 2.4.1.2 Problem Setup CHEMKIN has a pre-defined model for HCCI engine simulations. The model is called the Closed Internal Combustion Engine Simulator and we can select it either by dragand-dropping or by double-clicking on the reactor icon (see Figure 2-27). Figure 2-27 IC Engine Icon The next step is to define the chemistry set, or combustion mechanism, for our HCCI simulation. Since methane is the main component of natural gas, we can use GRI Mech 3.0, as described in section Section 2.8.2, to describe the combustion process. Once we successfully complete the pre-processor step, we can start to fill out the Reactor Properties (or C1_ IC Engine) panel with the engine specifications listed in Table 2-7. Since the HCCI model is for a closed system, the simulation is only valid within the time period when both intake and exhaust valves are closed. We need to find out when the intake valve is closed and use the gas properties at that moment as the initial conditions for our HCCI engine simulation. As a convention, engine events are expressed in crank rotation angle relative to the top dead center (TDC). The intake © 2007 Reaction Design 50 RD0411-C20-000-001
Chapter 2: Combustion in Gas-phase Processes <strong>Tutorials</strong> <strong>Manual</strong> valve close (IVC) time of our test engine is 142 degrees (crank angle) before TDC (BTDC). Accordingly, we should set our simulation starting crank angle to -142 degrees. We let the simulation run for 0.043 sec or for 257 degrees crank angle to 115 degrees after TDC. The gas mixture pressure and temperature at IVC are 107911 Pa (or 1.065 atm) and 447 K, respectively. The composition of the initial gas mixture is a combination of natural gas, air, and EGR gas and is given in Table 2-8. Table 2-8 Species Composition of Initial Gas Mixture Mole Fraction CH4 0.0350 C2H6 0.0018 C3H8 0.0012 O2 0.1824 CO2 0.0326 H2O 0.0609 N2 0.6861 The project file for this HCCI engine simulation problem is called ic_engine__hcci_heat_loss_methane.ckprj and is located in the samples41 directory. This project file actually contains two “sub-projects”: the ic_engine__hcci_adiabatic project assumes the cylinder is adiabatic and the other project, ic_engine__hcci_heat_loss_woschni, considers heat loss through the cylinder wall. By default CHEMKIN will append the new project to an existing project file if the name of the new project is different from the ones already saved in the file. Therefore, we can group similar projects into the same project file by saving those projects one by one to the same project filename. Heat transfer between the gas mixture inside the cylinder and the cylinder wall can be specified on the Reactor Physical Properties panel. For the adiabatic case, no heat transfer occurs between the gas and the wall. We can simply leave the text box corresponding to the heat loss entry blank because the heat loss value is set to zero by default. For non-adiabatic cases, we have several ways to describe the heat loss to the wall: a constant heat transfer rate (positive for heat loss to environment), a piecewise heat transfer rate profile, a user subroutine, or a heat transfer correlation. Here we choose the heat-transfer correlation for our HCCI problem. We also apply the Woschni correction 14 to get better estimates of gas velocity inside the cylinder. 14. J. B. Heywood, Internal Combustion Engines Fundamentals, McGraw-Hill Science/Engineering/Math, New York, 1988. RD0411-C20-000-001 51 © 2007 Reaction Design
Page 1 and 2: August 3, 2007 1:53 am Release 4.1.
Page 3 and 4: Chemkin 4.1.1 Contents Table of Con
Page 5 and 6: Chemkin 4.1.1 Tables List of Tables
Page 7 and 8: Tutorials Manual 4.1.1 Figures List
Page 9 and 10: List of Figures Tutorials Manual 2-
Page 11 and 12: List of Figures Tutorials Manual 4-
Page 13 and 14: Chemkin 4.1.1 1 1 Introduction The
Page 15 and 16: Chapter 1: Introduction Tutorials M
Page 17 and 18: Chemkin 4.1.1 2 2 Combustion in Gas
Page 19 and 20: Chapter 2: Combustion in Gas-phase
Page 49: Chapter 2: Combustion in Gas-phase
Page 91 and 92: Chemkin 4.1.1 3 3 Catalytic Process
Page 93 and 94: Chapter 3: Catalytic Processes Tuto
Page 101 and 102:
Chapter 3: Catalytic Processes Tuto
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Chemkin 4.1.1 4 4 Materials Problem
Page 117 and 118:
Chapter 4: Materials Problems Tutor
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Chemkin 4.1.1 5 5 Chemical Mechanis
Page 163 and 164:
Chapter 5: Chemical Mechanism Analy
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Tutorials Manual 4.1.1 Index Index
Page 179 and 180:
Index Tutorials Manual normalized s
show all

Tutorials Manual

Create successful ePaper yourself

Delete template?

Save as template?