Determine gas speed in inlet port

 

Assumptions:

 

*      At high engine speed the gas speed in the port is higher than the velocity of the fuel being sprayed from the injector

*      Engine speed is 3700 rev/min

*      100% VE

*      Valve open time is 260

*      Engine size is 1330 cc or 332 cc per cylinder

*      Inlet port average diameter is 1.3 or 3.3 cm which is 8.56 cm2

 

 

3700 rev

*

360

*

min

=

22000

=

22.2

min

 

rev

 

60 sec

 

sec

 

ms

 

The valve is open for 260 so

 

260

*

ms

=

11.7 ms

 

 

22.2

 

 

 

332 cm3

=

28.4 cm3

 

11.7 ms

 

ms

 

 

Through continuity, pushing a volume through a fixed orifice we get

 

28.4 cm3

*

1

=

3.31 cm

=

33 mm

(about 100 km/hr)

ms

 

8.56 cm2

 

ms

 

ms

 

The distance from the cylinder head face, where the injector tips should be, to the back of the valve is something like 75 mm so it would take in the order of 2.5 ms for the fuel charge to reach the valve throat.