SI ENGINES

FOUR STROKE

INTERNAL COMBUSTION ENGINESFOUR STROKE

TWO STROKE

TWO STROKE

Wankel engines

• 3 LOBE ROTOR WHICH IS DRIVEN ECCENTRICALLY IN A CASING & 3 VOLUMES ARE TRAPPED BETWEEN THE ROTOR AND THE CASING. THESE VOLUMES PERFORM INDUCTION, COMPRESSION, POWER & EXHAUST STROKES SEPERATELY.

• SEAL WEAR & HEAT TRANSFER ARE PROBLEM AREAS

ROTARY

Wankel Engine Four Strokes

Wankel Engine - Four Strokes

Wankel Engine Details

COMPRESSION RATIO

• It is the ratio between the cylinder volume above the piston at BDC (Vbdc) and the volume above the piston at TDC (Vtdc). Vbdc is Vtdc plus the swept cylinder volume (Vsw).

• This is the ratio between the total volume to the clearance volume in IC engines

compression ratio = ────────

Vsw + Vtdc

Vtdc

INTERNAL COMBUSTION ENGINES

Cylinder Swept Volume or Displacement Volume (Vc)

Vc = Cylinder Area x Stroke Length

Vc = Ac x L = (π/4.dc2) x L

where:

Vc = cylinder swept volume [usually cm3 (cc) or L ]

Ac = cylinder area [usually cm2 or mm2]

dc = cylinder diameter [usually cm or mm]

L = stroke length (distance between the TDC and BDC) [usually cm or mm]

BORE/STROKE RATIOThe ratio between the cylinder diameter/cylinder stroke called “bore/stroke” ratio. •A “bore/stroke" =1 is called square engine•A “bore/stroke" >1 is called over square engine, and is used in automotive engines•A “bore/stoke” <1 is called an under square engine, and is used in tractor engines

Engine Swept Volume (Ve):Ve = Combined Swept Volumes of all Engine Cylinders

Ve = n Vc

Ve = n Ac x L = (π/4.dc2) x L where n= no of cylinders

HORSEPOWER

• Power is measured in many other units besides horsepower, depending on location and application. Watts (W) and kilowatts (kW) are in common use worldwide. Less common measures include British thermal units per hour (Btu/hr) and foot-pound force per minute (ft-lbf/min).

DEFINITION OF HORSEPOWER

• Standard mechanical horsepower is defined as about 33,000 ft-lbf/min, or 745.7 watts. However, there are other definitions of horsepower. Some of these definitions refer to different ways of measuring power for a specific application.

Indicated Horsepower• Indicated horsepower (ihp) is the power

developed inside the combustion chambers during combustion. Indicated horsepower is always higher than brake horsepower, as some of the power developed in the cylinders is lost in overcoming the internal friction in the engine

• It is calculated from the pressures developed in the cylinders, measured by a device called an engine indicator – hence the name indicated horsepower.

Indicated Horsepower

• Indicated Horsepower,ihp:ihp = pmL a n

33,000 Where: pm= mep, lb/in2

L = stroke, ft a = piston area, in2

n = number of cycles per minute 33000 = ft-lb/min / hp (definition)