Design Process of Fuel Injector Intake Manifold and Fuel Rail

When Fuel if flowing in injector, it pushes injector in to intake manifold hole or this force will compress cushion. Additionally Crushing of Injector due to wrong injector installation height (48.66mm as shown)- if tolerance stack up analysis is wrong then injector cushion and O ring will be damaged and this will leads to fuel leakage.   

O ring selection for leakage prevention –

Following 2 parameters are calculated for leakage prevention.

Ø  Compression Ratio = Change in O ring Dia/free O ring Dia= (D-t)/D =3.5-2.9/3.5=18 %

Ø  Filling Ratio =O ring area /groove area=[π * (D/2)^2 ]/ [b*t]= [3.14*(3.5/2)^2]/[4*2.9]=82%

Injector sitting whole dimension have fixed reference:

1.    Fix mounting hole of Rail on Intake Manifold for dimension measurement 

2.    Fix Intake Manifold mounting hole on Cylinder Head for dimension measurement    

Manifold Design	Spec mm	Remark
Injector O Ring D / d	15.2 / 3.5	Used for Intake Grove Design
Injector sitting area tolerance	+/-0.1	On surface b, z, d4 surface
Injector sitting surface finish	Ra 6.3	On surface b, z,a,d4 surface
Chamfer  Angle (α)	25 ° +/- 1	To avoid cutting of O Ring
Chamfer Height z	2 + 0.5/ -0
Stopper Surface for Injector	7 +/- 0.23	Injector O Ring cannot slide in to intake hole

Generally 4-5 bar ia pressure in gasoline fuel system and when high pressure fuel if flowing in injector, it pushes injector in to intake manifold hole or this force will compress cushion. Now due to this fuel pressure injector press the cushion fitted in intake manifold groove. To prevent this many fuel injector has clip - in next article we will learn how to design clip for fuel injector. 

Ø  Compression Ratio = Change in O ring Dia/free O ring Dia= (D-t)/D =3.5-2.9/3.5=18 %

Ø  Filling Ratio =O ring area /groove area=[π * (D/2)^2 ]/ [b*t]= [3.14*(3.5/2)^2]/[4*2.9]=82%

For background, please read previous blog and for further design process read next blog. 

Next topic is related to wall wetting and tolerances

Intake Runner Wall and Valve Wetting –

Fuel can go on runner wall or Valve stem; for better mixing of air and fuel spray angle of injector is optimized. In case of single port and two intakes valve if injector physically rotate this may leads to valve wetting.