The order in which the multi-cylinder engine will deliver power is called the firing order of a particular machine.

**Firing order is a critical parameter to get optimum performance of an engine. The order will affect the amount of vibration, generation of back pressure, proper balancing of the engine, smooth flow of power, and the cooling rate of the engine. This article discusses how to determine firing order of engine.**

**Firing order in multi cylinder engine**

Multi cylinder engines have many cylinders stacked next to each other. The question arises that which cylinder should be fired and when?

If the cylinders are fired randomly then there is high probability that the engine will suffer catastrophic failure. The reasons of failure due to improper firing include- high vibrations, high heat dissipation and excess load on bearing. Hence, an optimum firing order is calculated to overcome engine failure.

**Typical firing orders of four cylinder engine are- 1-3-4-2, 1-4-3-2, 1-4-2-3 etc.****Typical firing orders of five cylinder engines are- 1-2-4-5-3 , 1-4-5-2-4 etc**.**Typical firing orders of six cylinder engines are- 1-3-5-2-4-6, 1-4-2-5-3-6 etc.**

## Formula to calculate firing order of IC engine

We can formulate the firing order of the IC engine in such a manner that it will give optimum results for n number of cylinders. The firing interval can be calculated by dividing 720 degrees by the number of cylinders and then giving the proper order.

**Let us formulate the firing order for an inline four-cylinder IC engine.**

**Number the cylinder as follow: 1, 2, 3, 4**

**The firing interval in the cylinder will be at:**

**Firing interval = 720/n = 720/4 = 180 degree**

We will assume the cylinder’s alignment will be so that 1 and cylinder 4 will have the same motion and cylinder 2 and 3 will have the same motion.

We can formulate it simple by putting it in a tabular manner.

Let us consider if we put firing of 1st cylinder at 1st position, then the last cylinder, the fourth cylinder, will have the suction operation at the time.

now we have two options, as we know that the motion of the 2nd and 3rd cylinder is going to in the same manner, but we don’t know exactly what action will it carry out to give the optimum solution.

**We can formulate the firing order of IC engine using method discussed in above section. There can be multiple ways by which the firing sequence can take place. Let us consider following options-**

**Option 1: to give compression at 2nd cylinder and exhaust at 3rd cylinder**

**At the 1st interval, the action will be as follow: **

Power – compression – exhaust – suction

That is, when cylinder one is going to have power stroke means it is moving downward, the second cylinder will be going upward as it is following the opposite manner causing the compression. The third cylinder will have action same action as 2nd cylinder and will carry out the exhaust action, and the fourth cylinder will carry out the action similar to 1st cylinder with the operation of suction.

This will take place at the 1st interval, and for 2nd interval, each action of the cylinder will be forwarded to their sequential second operation

**For the second interval we will have the following action:**

1st cylinder will have an exhaust stroke, the 2nd cylinder will have a power stroke, the 3rd stroke will have a suction stroke, and the 4th cylinder will have a compression stroke.

**For the third interval, we will have the following action:**

1st cylinder will have a suction stroke, the 2nd cylinder will have an exhaust stroke, the 3rd stroke will have a compression stroke, and the 4th cylinder will have a power stroke.

**For fourth interval we will have the following action:**

1st cylinder will have a compression stroke, the 2nd cylinder will have a suction stroke, the 3rd stroke will have a power stroke, and the 4th cylinder will have an exhaust stroke.

**Option 2: to give exhaust at 2nd cylinder and compression at 3rd cylinder**

**At the 1st interval, the action will be as follow:**

Power – exhaust – compression – suction

That is when the cylinder one is going to have a power stroke means it is moving downward. The second cylinder will be going upward as it is following the same manner, causing the exhaust. The third cylinder will have action same action as the 2nd cylinder and will carry out compression action. The fourth cylinder will carry out the action similar to the 1st cylinder with the operation of suction.

This will take place at the 1st interval, and for 2nd interval, each action of the cylinder will be forwarded to their sequential second operation

**For the second interval, we will have the following action:**

1st cylinder will have an exhaust stroke, and 2nd cylinder will have a suction stroke; 3rd stroke will have a power stroke, and the 4th cylinder will have a compression stroke.

**For the third interval, we will have the following action:**

1st cylinder will have a suction stroke, and 2nd cylinder will have a compression stroke; 3rd stroke will have an exhaust stroke, and the 4th cylinder will have a power stroke.

**For the fourth interval, we will have the following action:**

1st cylinder will have a compression stroke, and 2nd cylinder will have a power stroke; 3rd stroke will have a suction stroke, and the 4th cylinder will have an exhaust stroke.

Now we know the order of the operation to be carried out

**As operation will follow the cycle of : **

**Suction to compression **

**Compression to power **

**Power and then exhaust **

**And again, exhaust to suction**

This process sequence is not going to change in any manner, so we can get the result very easily.

So with option 1, we will get the following result:

With this, the firing order will be: 1-2-4-3

So with option 2, we will get the following result:

**With this the firing order will be: 1-3-4-2**

So now we have two options. Which will be good or optimum?

We must remember that if we give firing next correct in sequence, it will give more vibration than the other one. Even though both will work well then too, we need to choose best.

So in this condition, we will go with option 2.

That is firing order: 1-3-4-2

Similarly, we can find the firing order of any number of cylinders.

**Following are some firing orders used by automobiles:**

**3 cylinder: **

**1-2-3 for perodua engine****1-3-2 for BMW K75 engine, Subaru Justy engine**

**4 cylinder**

**1-3-2-4 for Ford Taunus V4 engine****1-2-4-3 for British Ford and relay engine****1-3-2-4 for Yamaha R1 cross-plane, Subaru 4-cylinder engines****1-4-3-2 for Volkswagen air-cooled engine**

**5 cylinder**

**1-2-4-5-3 for Straight-five engine, Volvo 850, Audi 100****1-3-5-4-2 for GM Atlas engine**

**6 cylinder**

**1-5-3-6-2-4 for Volkswagen VR6 engine, Opel Omega A, Nissan L Engine****1-4-3-6-2-5 for Mercedes-Benz M272 engine****1-6-5-4-3-2 for GM 3800 engine, Rover KV6 engine****1-2-3-4-5-6 for Chrysler Pentastar engine****1-4-2-5-3-6 for Ford Cologne V6 engine, Ford Essex V6 engine (UK)****1-4-2-6-3-5 for Toyota HZ engine**.