Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
The required reed flow area past the petals, Arcj, is given by determining the area of an
isosceles triangle of opening which spans an assumed period, 6p, of 200°:
A _ _J 2fAd6 _ 12A V
rd =
1 ^ rv svi v sv rpm
e. er
m (6.3.2)
At this point the designer has to estimate values for the reed port dimensions and determine
a flow area which will match that required from the time-area analysis. That step is to
assign numbers to the reed port dimensions shown in Fig. 5.4, and is found from Eq. 5.2.18.
The notation for the data is also given in Fig. 6.27. The effective reed port area is declared as
Ar
*rp-
Arp - n rp( L P X P " rD 2 (4 rc))sinrb (6.3.3)
The required reed flow area, A,p, and the port area, Ar(j, are compared and the port dimensions
adjusted until the two values match from Eqs. 6.3.2 and 6.3.3. If anything, you should
always err slightly on the generous side in apportioning reed port area. Without carrying out
this form of design calculation, one tends to err on the restrictive side because the eye, viewing
it on a drawing board or a CAD screen, tends to see the projected plan area and not the allimportant
effective area in the flow direction.
CYLINDER Vsv, cc= 125 SPEED, rpm=
PETAL MATERIAL IS GLASS-FIBRE
PETAL THICKNESS , Xf, mm= .42
REED BLOCK ANGLE 'PHIrb', deg= 23.5
PETAL NUMBER 'Nf = 6
PORTS NUMBER'Np'= 6
PETAL WIDTH'Xr", mm= 22.7
PORT WIDTH •Xp', mm= 19.6
CORNER RADIUS'Rp', mm= 1
PETAL LENGTH "Lr', mm= 3 8
PORT LENGTH'Lp', mm= 3 2
LENGTH FROM CLAMP 'Xs', mm= 4
OUTPUT DATA
Asvi requi red area, mm2=1396.
PORT AREA 'Arp', mm2=1499.
REED AREA 'Ard', mm2=1474.
CARBURETTER, 'Dtv', mm= 38.
REED NATURAL FREQUENCY, Hz= 1 6 0.
ENGINE NATURAL FREQUENCY, Hz= 192.
TIP LIFT RATIO, 'Crdt'=0.33
STOP PLATE RADIUS 'Rsp', mm= 58.
11500 bmep, bar= 11 CRcc= 1.35
SECTION ON HALF BLOCK
PLAN ON PORT AND PETAL OUTLINE
DARK AREA IS CLAMP FOOTPRINT
Fig. 6.27 Computer screen output from Prog.6.4, REED VALVE DESIGN.
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