1. Measure of Filling & Emptying Effectiveness….
Engine Breathing
P M V Subbarao
Professor
Mechanical Engineering Department
Measure of Filling & Emptying Effectiveness….

2. A Global Measure of Breathing Effectiveness
Volumetric efficiency a measure of overall effectiveness of engine and its intake and exhaust system as a natural breathing system.
Volumetric efficiency is defined as:

3. Significance of Reference Density
If the air density a,0 is evaluated at inlet manifold conditions, the volumetric efficiency is a measure of breathing performance of the cylinder, inlet port and valve.
If the air density a,0 is evaluated at ambient conditions, the volumetric efficiency is a measure of overall intake and exhaust system and other engine features.
The full load value of volumetric efficiency is a design feature of entire engine system.

4. Engine Respiratory System

5. Transient Pressure in manifolds & Cylinder
Exhaust Pipe 3 2 1

6. Transient Pressure in Manifolds
1200RPM
4800RPM

7. Computation of Intake Process : SI Engine
FUEL
SI Engine

8. Instantaneous Heat Transfer During Intake Process

9. Total Mass of mixture inhaled during Intake Process
FUEL

10. Instantaneous mass flow Rate and Cumulate Mass

11. Computation of Exhaust Process : SI Engine
Combustion
Products
Exhaust
Stroke

13. Stream Tube formed by Flow Through Valves
Equivalent Converging-Diverging Nozzle Configurations:
Mild Separation.
Severe Separation

14. Instantaneous minimum Available Flow area: Low Lift
For low lift valves, the minimum available flow area corresponds to a frustum of right circular cone.
The annular space between valve and seat forms the minimum flow area perpendicular to the seat.
The range of valve lift for generation of right angle cones
The minimum area is:

15. Instantaneous minimum Available Flow area : Intermediate Lift
For the second stage, the minimum area is still the frustum of a right circular cone.
However, this flow area is not perpendicular to the valve seat.
The base angle of the cone increases from (900-) toward that of a cylinder.
For range of valve lift for this stage:
Dm is mean diameter of seat :

16. Instantaneous minimum Available Flow area : High Lift
When the valve lift is sufficiently large, the minimum flow area is no longer between the valve head and seat.
It is the port area minus the sectional area of the valve stem.
Then,

17. Valve Lift Vs Flow Area Curves