1. Technical knowledge Series Two wheelers - BikeJinni
By Dhriti

2. 1.Engine Classification-
1.1 Spark Ignition Engines
1.2 Compression Ignition Engines
1.3 Two stroke & Four stroke Engines
1.4 Engine Types – Vertical, Horizontal,
Inline , V Engine etc
1.5 OHC and DOHC Engines

3. 1.1 Spark Ignition (SI) Engines
In Spark Ignition Engine or SI Engine- Air-fuel mixture enters into the combustion chamber together. ignition takes place with the help of an electric spark by spark plug.
Usually petrol engines are SI engines.
Spark Ignition Engine

4. 1.2 Compression Ignition (CI) Engines
In Compression Ignition Engine or CI Engine -Air and fuel enters separately into the combustion chamber. Ignition takes place by means of heat generated by the compressed air inside the cylinder.
There is no spark plug
Diesel engines are CI engines

5. 1.3 Two Stroke Engines In Two Stroke Engine -
First stroke: is combination of Intake & Compression stroke .
Piston moves up to compress the air/fuel mixture, at the same time intake port is opened which allows fresh mixture to move in the lower part of crankcase. Transfer port helps in moving this fresh mixture from the lower portion to the top of the piston.
Second stroke: This stroke is a combination of power and exhaust strokes. The piston moves down after power stroke, opening the exhaust port at the same time to move burnt gases out of the combustion space. 
Second Stroke
Power & Exhaust
First Stroke
Intake & Compression

6. 1.4 Four Stroke Engine In Four Stroke Engine -
First is Intake Stroke: Inlet valve is open and the fuel air mixture is drawn in while the piston goes down.
Second is Compression Stroke: Inlet valve is closed and piston moves up, thus compressing the fuel air mixture Before the piston reaches the top the spark plug emits a spark that combust the fuel air mixture.
Third is Combustion Stroke: The piston is forced down due to Combustion of fuel air mixture. Engine power is obtained from this.
Exhaust Stroke: Exhaust valve is open and the piston travels up making the gases to exit from the exhaust valve.

7. 1.5 Vertical , Horizontal , Inline , V-Type Engines
Based on the design of chassis of the bike different types of Engines are used.
1. Vertical Engine –
Piston movies vertically up & down. Crankshaft is below the cylinder.
Convenient to orient cylinder vertically since they are taller.
Space around cannot be used.
2. Horizontal Engine –
Cylinder is placed horizontally.
Less Power loss , Better handling. Packing size is more since very wide.
3. Inline Engine –
Banks of cylinder are placed one behind the other. Mainly six cylinder in
one bank are used.
Simpler, Lighter. Longer & Skinny , Hard to pack.
4. V Engine –
Two rows of cylinder at 90 deg angle to each other are placed.
Short length , easier to fir. But , separate cam shafts for each
side of the V makes it complex.
Vertical Engine
Horizontal
Engine
Inline Engine
V Engine

8. 1.6 OHC and DOHC Engines
A camshaft rotates and its lobes open and close the valves in time with the piston to allow air in and exhaust out down to enable combustion cycle of an engine. Commonly ,there are two type of Camshaft arrangement-
Double Cam
Single Cam
SOHC = Single Overhead Camshaft
DOHC = Double Overhead Camshaft
In a SOHC engine , the camshaft is installed in the cylinder head. Valves are operated either by the rocker arms or directly through the lobe lifters of rotating camshaft.
DOHC engine normally has two camshafts and 4 valves per cylinder. One side camshaft operates intake valves, while opposite side camshaft controls exhaust valves. 
SOHC engines are less complicated in design & cheaper. DOHC engines rev much higher and develop more power at mid to top rpms for the same displacement engine. DOHC engines are ideal for performance or Sports racing bikes , while these are cooler ,runs more smoothly, quietly, and efficiently.

9. Engine – Technical Terms and Parts
2.Engine Technical Terms & Parts-
2.1 Engine – Bore & Stroke
2.2 Engine – Compression Ratio
2.3 Engine – Maximum Power and Torque
2.4 Capacitor Discharged Ignition (CDI)
2.5 Spark plug
2.6 Valve
2.7 Engine- Cooling System

10. Engine – Bore & Stroke Bore : It is the diameter of the cylinder.
Stroke : It is the distance to which piston travels.
What is cc (Cubic Centimetre) ?
Volume of Cylinder : Normally more the Volume of Cylinder of an Engine,
more Power it can produce.
Displacement/Swept Volume of an engine (V) = pi * S * B^2 / 4
Larger the bore and stroke, the bigger the  displacement and thus a
more power of engine.
Unit is CC or Litre . CC stands for Cubic Centimetres cc = 1 litre.

11. Engine – Compression Ratio
It's the ratio of the volume of the combustion chamber and bore when the piston is at bottom dead centre (BDC) versus when it is at top dead centre (TDC).
Formula - (Swept Volume + Clearance Volume) / Clearance Volume
Swept Volume = pi * S * B^2 / 4
Clearance Volume = Above the piston at TDC is the volume contained in the cylinder head gasket and combustion chamber - this volume is called the "Clearance Volume".

12. Engine – Maximum Power and Torque
Torque :Twisting or turning force
Automotive terms - It is a rotating force produced by an engine’s crankshaft.
Unit is Newton metre (Nm)
The more torque an engine produces, the greater its ability to perform work.
Formula : Torque = 5252 x Horsepower / RPM
RPM (Revolution per Minute) = Speed at which the crank shaft is rotating , if you accelerate the RPM will increase.
Power: How fast can engine do work
Normal used Units are BHP , Ps ,Kw.
I Ps = newton·m/s ~= W ~= kW ~= hp

13. Capacitor Discharged Ignition (CDI)
The capacitor discharged ignition uses capacitor discharge current output to power the spark plug for a powerful ,high spark.
It stores current. Stored current is divided to give it to other parts of the vehicle .
If current exceeds the limit in the battery, CDI becomes hot and vehicle stops. After CDI cools vehicle may or may not start.

14. Spark plug
A device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark.
First Stroke
Intake & Compression
Spark Plug

15. Valve
Two types-
1.It allows mixture into the cylinder is the inlet valve.
2.The one through which the spent gases escape is the exhaust valve.
They are designed to open and close at precise moments, to allow the engine to run efficiently at all speeds.
An OHC (or DOHC) Engine cylinder head will have at least two valves per cylinder (1 inlet and 1 exhaust), but multi-valve engines may have three (2 inlet and 1 exhaust), or four (2 inlet and 2 exhaust), five (3 inlet and 2 exhaust) or even more . Multi-valve engines rev higher and make more , while have more components resulting higher cost.
Two Valve – Engine
Three Valve – Engine
Four Valve – Engine

16. Engine- Cooling System
Cooling System – It prevents engine breakdown due to overheating.
1. Air cooled Engines –
Engine of the motorcycle is cooled naturally by the outside atmosphere air.
2. Liquid cooled Engines –
Engine is surrounded by the liquid cooling system. It uses a coolant to keep the temperature of the engine at an optimum level.
Air Cooled Engine
Liquid Cooled Engine

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