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THE FOUR STROKE CYCLE BUT HOW DOES IT WORK EXACTLY? 1. INDUCTION 4. EXHAUST 3. COMBUSTION 2. COMPRESSION SUCK BLOW BANG SQUEEZE WE KNOW ABOUT:- WHICH WE.

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Presentation on theme: "THE FOUR STROKE CYCLE BUT HOW DOES IT WORK EXACTLY? 1. INDUCTION 4. EXHAUST 3. COMBUSTION 2. COMPRESSION SUCK BLOW BANG SQUEEZE WE KNOW ABOUT:- WHICH WE."— Presentation transcript:

1 THE FOUR STROKE CYCLE BUT HOW DOES IT WORK EXACTLY? 1. INDUCTION 4. EXHAUST 3. COMBUSTION 2. COMPRESSION SUCK BLOW BANG SQUEEZE WE KNOW ABOUT:- WHICH WE KNOW AS:- LET’S LOOK IN MORE DETAIL

2 WE’LL SEE A STEP BY STEP EXPLAINATION OF THIS DIAGRAM AND RELATE IT TO THIS DIAGRAM Operating Cycle

3 AND THIS DIAGRAM 1 ‘Stroke’ = the piston sliding either up or down the cylinder Therefore a ‘Four’ Stroke engine is 2 revs of the crankshaft Down Down Up Up

4 TDC BDC STROKE 1 PISTON MOVES DOWN CYLINDER CRANK ROTATES AIR/FUEL DRAWN (INDUCED - SUCKED) INTO CYLINDER Operating Cycle

5 TDC BDC STROKE 2 PISTON MOVES BACK UP CYLINDER AIR/FUEL TRAPPED (COMPRESSED - SQUEEZED) IN CYLINDER CRANK CONTINUES TO ROTATE Operating Cycle

6 TDC BDC STROKE 3 PISTON FORCED DOWN CYLINDER CRANK STARTS 2ND ROTATION AIR/FUEL IGNITED AND BURNS (COMBUSTION - BLOW) IN CYLINDER Operating Cycle

7 TDC BDC STROKE 4 PISTON MOVES BACK UP CYLINDER AGAIN CRANK CONTINUES 2 ND ROTATION BURNT AIR/FUEL PUSHED OUT OF CYLINDER (EXHAUST – BLOW) Operating Cycle

8 When the end of the exhaust stroke is reached It is of course the start of the induction stroke And the whole process starts again Operating Cycle

9 But :- Because valves don’t open and close instantly, and the air/fuel mixture doesn’t explode instantly (it’s a rapid burning process) valve operation and air/fuel ignition isn’t set at the TDC and BDC positions. These events are set to occur at the following positions, designated as angular positions of the crank shaft. Operating Cycle

10 We’ll start the process at 30 degrees before TDC The start of Induction – Stroke 1 TDC BDC At which point, the Inlet valve begins to open Operating Cycle

11 The induction stroke ends at 15 degrees after BDC. TDC BDC Trapping the air/fuel mixture in the cylinder When the Inlet valve closes 1. Induction Inlet valve closes Inlet valve opens Called Valve Lag because it is after BDC Operating Cycle The start of Compression – Stroke 2

12 Ignition occurs at 30 degrees before TDC. And is the start of the Power stroke At this point, both valves are closed TDC BDC Inlet valve closes 1. Induction 2. Compression Inlet valve opens Ignition Operating Cycle The start of Power – Stroke 3

13 Burning air/fuel mixture reaches maximum expansion And is the end of the Power stroke and start of the Exhaust stroke TDC BDC Inlet valve closes 1. Induction 2. Compression Inlet valve opens Ignition 3. Power 15 degrees before BDC, the exhaust valve opens Exhaust valve opens Called Valve Lead because it is before BDC The start of Exhaust – Stroke 4 Operating Cycle

14 This position is towards the end of the Exhaust stroke And is ALSO the beginning of the Induction stroke TDC BDC Inlet valve closes 1. Induction 2. Compression Inlet valve opens Ignition 3. Power Exhaust valve opens 4. Exhaust the inlet valve starts to open So as the exhaust valve starts to close, Operating Cycle The end of Exhaust – Stroke 4

15 ‘Valve Overlap’ This is called ‘Valve Overlap’ TDC BDC Inlet valve closes 1. Induction 2. Compression Inlet valve opens Ignition 3. Power 4. Exhaust Both the inlet and exhaust valves are partially open Exhaust valve closes 45 degrees before Therefore the Induction stroke starts 45 degrees before the end of the Exhaust stroke Operating Cycle Valve Overlap - Stroke 4 to 1 Exhaust valve opens

16 This position is at the end of the exhaust stroke And is 45 degrees into the induction stroke TDC BDC Inlet valve closes 1. Induction 2. Compression Inlet valve opens Ignition 3. Power 4. Exhaust The inlet valve is now open The exhaust valve is now closed Exhaust valve closes Operating Cycle Exhaust valve opens The start of Induction – Stroke 1

17 Simple isn’t it! Suck Squeeze Bang Blow Operating Cycle

18 in all 4 stroke engines no matter how many cylinders there are. Lets look at the most typical vehicle engine, the ‘Inline 4’ But, this is happening in every cylinder Operating Cycle

19 The cylinders are numbered from the front to the rear And the firing order is:- 1 – 3 – Operating Cycle

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