Tutorials Manual

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
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