Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
To assist with the analysis of computed data, and to compare it with that measured, it is
useful to declare a reed tip lift ratio, Crdt, defined at any instant with respect to the reed
length, as:
-rdt Lr
(5.2.20)
The empirical solution for reed valve design, given in Sec. 6.3, may help to further elucidate
you about the application of some of the theory shown here.
5.2.3 The intake ducting
The intake ducting must be designed to suit the type of induction system, i.e., be it by reed
valve, or be it piston skirt controlled, or through the use of a disc valve, all of which have been
discussed initially in Sec. 1.3. The modeling of the port has been discussed above.
A typical intake duct is shown in Fig. 5.5. It commences at the inlet port, marked as Ajp,
and extends to the atmosphere at an inlet silencer box of volume, VIB, and breathes through
an air filter of effective diameter, dp. The area of the inlet port, AIP, is normally the area seen
in Sec. 5.2 described as the maximum area at the cylinder or crankcase port, Amax, but is not
necessarily so for it is not uncommon in practice that there is a step change at that position.
The point is best made by re-examining Figs. 2.16 and 2.18, as the area at the end of the intake
system denoted here by Aip is actually the area denoted by A2 in Figs. 2.16 and 2.18. It is
good design practice to ensure that A2, i.e., Ajp, precisely equals the maximum port area; it is
not always seen in production engines. Should the engine have a reed valve intake system,
then it is normal for Ajp to equal the value defined as such in Eq. 5.2.17. Should the engine
have a disc valve intake system, then it is normal for Ajp to equal the value defined as Amax in
Eq. 5.2.9.
Somewhere within this intake duct there will be a throttle, or combined throttle and venturi
if included with a carburetor, of effective diameter, dtv- The throttle and venturi are modeled
using the restricted pipe theory from Sec. 2.12. All of the other pipe sections, of lengths
Li, L2, and L4, with diameters ranging from do which is equivalent to area An>, to di, d2, d3,
and d4, are modeled using the tapered pipe theory found in Sec. 2.15.
Fig. 5.5 Dimensions of an intake system including the carburetor.
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