ENGINE MECHANICAL MEASUREMENTS

 ENGINE MECHANICAL MEASUREMENTS

Engine performance often depends on mechanical measurements of the engine. These include bore and stroke, piston displacement and compression ratio. The mechanical measurement greatly affects engine torque and power. they also affect operating range or speed.

What are car/bikes CC means? 

CC stand for cubic centimetre is sometimes called engine capacity. Cubic Centimeter (CC) represent the total volume of air and fuel drawn through the engine by the cylinder ers.

The internal combustion (IC) engine size of an engine cylinder is given by its bore and stroke.

ENGINE BORE, STROKE AND PISTON DISPLACEMENT

The internal diameter of the engine cylinder is called a bore. Bore is always first given an engine measured.

In an engine cylinder, the distance that piston move travelling from the Bottom Dead Centre (BDC) to Top Dead Centre (TDC). is called stroke 

An engine cylinder piston displacement is the volume the piston displace as it moves from BDC to TDC.

For example:

 the piston displacement in a 4 by 3.5 inch (101.6 by 88.9mm), the bore is 4 inches and stroke is 3.1/2 inches.

In other words to understand that, Engine in term of the ratio of the volume of air and fuel in the engine cylinder 4 inches in diameter and 3.5 inches length (long).

To find the piston displacement of this cylinder, use the formula. πxDxDxL

 = 3.14XDXDXL/     = 3.14X4X4X3.5/4

 = 3.14 X16X3.5/4  = 43.96 cubic inches.

One cubic inch equal 16.39 cc

One liter is 61.02 cubic inches.

 Compression Ratio (CR)

The volume of the cylinder and combustion chamber when the piston is at BDC, divided by the volume when the piston is at TDC. The measure of how air-fuel mixture or air is compressed during the compression stroke.

A simple way to understand, The air volume in the cylinder with the piston at the bottom dead centre (BDC) divided by the clearance volume. The volume with the piston at TDC is the clearance volume.

For example, one engine has a cylinder volume of 42.35 cubic inches(694cc)at BDC. It has a clearance volume of 4.45cubic inches (73 ccs). The compression ratio is 42.35 divided by 4.45 (694/73). This is 9.5:1. The air-fuel mixture is compressed to 1/9.5 of its original volume during the compression stroke.

Volumetric Efficiency (VE)

The amount of the air-fuel mixture taken in by the engine cylinder on the intake stroke (suction stroke) of the spark-ignition engine is a measure of the engine is called volumetric efficiency.

Good volumetric efficiency for an engine running at fairly high speed is 80 per cent. The VE of some engines at high speed may drop to 50% .this means the cylinder are only half-filled. The decrease in VE is one reason that engine speed and power do not continue to increase. Another action that affects VE is how quickly and easily the burned gases exhaust from the cylinder. Exhaust gases remain in the cylinder after the intake (suction ) stroke begins to allow the less air-fuel mixture to enter. 

There are several ways to improve volumetric efficiency.

* to uses larger intake valves.

* to use more than one intake/exhaust valves  per cylinder ( multiple valves

   per cylinder means, the use of four valves - two intakes and two exhaust per cylinder).

* to improve engine performance is Forced Induction device like turbocharger and supercharger.

* tuned intake and exhaust manifold. (tuning the manifold to improving volumetric efficiency.

* power and torque are also mattered for the volumetric efficiency higher compression pressure, the great the torque and power.