<div class = text-justify>
Hello, I Hope you all are fine and I welcome you to my blog once again and thanks for the constant encouragement.

I started a series which I would love to continue here, the aim of the series is for those of us who are planning to get a mechanical machine that has an engine and don't know what we are going for and you would want to know what is up in the market and also make the right decision that suit your personality (funny enough a dealer with not go this dip explaining what is inside a car) in one word choose what would work for you. You can see the first part of this series [here](https://steemit.com/stemng/@osariemen/different-mechanism-and-classification-of-automobile-engines) , in the article 2 Classifications of an engine were discussed which are the Classification by fuel and Classification by Combustion.

On this Post I will be doing justice to the the classification by [ignition](https://www.google.com.ng/search?client=ms-android-transsion&ei=n-YDW-riEcLIgAbx8aKACw&q=ignition+meaning&oq=ignition+meaning&gs_l=mobile-gws-wiz-serp.3..0i67i70i249j0l4.3370.7496..10369...1....428.3665.3-8j2......0....1.........0i71j0i67j0i22i30j0i13i70i249j0i13.RWVQuWq43zQ%3D) and the classification by engine strokes.

## Introduction
Engines in mechanical machines works differently as I have said in the previous post and the difference here will be based ignition of the vehicle and the stroke of engines, first of all little explanation about ignition, ignition is the process of beginning the combustion of fuel (either diesel or petrol) and engines strokes is the stages or in mechanical terms strokes the engine takes to start (which can be either 2 or 4 strokes in different cases I would explain)  

![czech-1354173__480.jpg](https://steemitimages.com/DQmRDDwwZvybyB6dyokofdfwa8UxcengR1Wm1i7ATbH3KXm/czech-1354173__480.jpg)<center><sub>image source: pixabay [link CC0 Licensed](pixabay.com)</sub></center>

#### Classification by Ignition
Before I go into the Classification proper, lets see what the meaning of ignition is from Google dictionary. 
>the process of starting the combustion of fuel in the engine cylinders.<sub>[source](https://www.google.com.ng/search?client=ms-android-transsion&ei=n-YDW-riEcLIgAbx8aKACw&q=ignition+meaning&oq=ignition+meaning&gs_l=mobile-gws-wiz-serp.3..0i67i70i249j0l4.3370.7496..10369...1....428.3665.3-8j2......0....1.........0i71j0i67j0i22i30j0i13i70i249j0i13.RWVQuWq43zQ%3D)</sub>

Engine ignition can be in Spark ignition engines and Compression ignition engine, the Major difference about their two type of ignition Is that Spark ignition engine runs on Otto cycle while the Compression ignition runs on Diesel Cycle, it's not that big of a term Otto cycle is the petrol engine while the Diesel Cycle runs on Diesel engine. 

#### <center>Difference in Spark ignition and Compression ignition</center>

* **Engine Speed:** The Spark Ignition engines are high speed engines because the fuel is burnt homogeneously while the Compression ignition engines are low speed engines because the fuel burnt heterogeneously. 

* **Type of Cycle:** The Spark ignition engine works with Otto cycle while the Compression ignition engine works with diesel cycle. 

[Otto cycle](https://en.m.wikipedia.org/wiki/Otto_cycle) is associated the petrol engine common is most if the automobiles today and it mode of fire uses the SPARK PLUG like the name Spark ignition 

While 

[Diesel Cycle](https://en.m.wikipedia.org/wiki/Diesel_cycle) Is associated with the diesel engine, the diesel is ignited by the heat generated when the compression of air in the combustion chamber, into which the diesel is injected. 

* **Thermal Efficiency:** Thermal efficiency of the spark ignition engine is Low due to the lower compression ratio of the combustion process while the Thermal efficiency of the Compression Ignition engine is high due to the higher compression ration of the combustion process 

#### Other difference in Spark ignition and Compression ignition Below 

<div class="pull-right">

## Spark ignition 

![Volkswagen_W16.jpg](https://steemitimages.com/DQmQhMMLKr9sCJAuasEyx9SQhS7CtYwmHXtiqAT6ae2FkYM/Volkswagen_W16.jpg) <sub>[Wikipedia CC 3.0 Licensed](https://en.m.wikipedia.org/wiki/Petrol_engine)</sub> 

<hr>
<hr>
<hr>
<hr>

* **Time of Knocking**

`Knocking happens at the end of combustion`

* **Type of fuel used**

`Petrol `

* **Constant Parameter in Cycle**

`Volume is constant `

* **Maintenance cost**

`Low cost`

* **Noise Production**

`Low noise `

* **Vibration problem**

`Low`

* **Cost of Engine**

`Low cost`

* **Fuel supply**

`Carburetor`

* **Application**

`light vehicles like motorcycle, cars for commercial use`

</div>

<div class="pull-left">

## Compression ignition 

![Fairbanks_Morse_model_32.jpg](https://steemitimages.com/DQmPSvv7WiGUoRGBTLQdgJkr3jvU3ynwFjBNUu7PXf5zC1G/Fairbanks_Morse_model_32.jpg) <sub>[Wikipedia CC 3.0 Licensed](https://en.m.wikipedia.org/wiki/Diesel_engine)</sub>  

* **Time of Knocking**

`Knocking happens at the beginning of combustion `

* **Type of fuel used** 

`Diesel `

* **Constant Parameter in Cycle**

`Pressure is constant `

* **Maintenance cost**

`High cost`

* **Noise Production**

`High Noise`

* **Vibration problem**

`Very High`

* **Cost of Engine**

`High cost`

* **Fuel supply**

`injector`

* **Application**

`Heavy lifting vehicles like trucks and industry generators`
</div>


<hr>

### <center>Classification by engine stroke</center>

Majorly engine strokes are in 4 strokes and 2 strokes, Engine stroke is the combustion stages for the  engine to start, actual term is the strokes taken to start the engine and it is in four stages which are the intake, compression, firing and the exhaust. This stages happen in both the 2 stroke and 4 Stroke but for the 4 Stroke it all happen in 4 Stroke while for the 2 stroke engine it happens in 2 stroke. 

>A stroke refers to the full travel of the piston along the cylinder, in either direction.<sub>[source](https://www.google.com.ng/search?q=engine+stroke+meaning&oq=engine+stroke+meaning&aqs=chrome..69i57j0l3&client=ms-android-transsion&sourceid=chrome-mobile&ie=UTF-8)</sub>

The 4 Stroke Engines are found in some cars, big generator, and some busses for commercial while the 2 stroke engines are found in the small engines like the little generators used in small apartments and then we can fine the 2 stroke engines in some motorcycles. 

#### <center>How the 2 Stroke engine works</center>

![2-Stroke_Engine_ani.gif](https://steemitimages.com/DQmXhL8hqjgZtKYkJ6BRDess8GCZvg8ipVbt52ZYTdLxAvy/2-Stroke_Engine_ani.gif)
<sub>[Wikipedia CC 3.0 Licensed](https://en.m.wikipedia.org/wiki/Two-stroke_engine)</sub>  

The 2 stroke engine as written above takes 2 strokes to get the engine started. The intake, compression, power and exhaust stroke happen in 2stroke which is the downstroke and Upstroke. 

(1)  Downstroke:
The downstroke is the stroke where air and fuel mixture is sucked into the combustion chamber for combustion and it takes place when piston move from the top dead center to the bottom dead center along side with the crankshaft rotating 180<sup>o</sup>

(2)Upstroke: 
The upstroke is where the remaining stages happens starting from the Piston moving back to the top dead center from the bottom dead center with the help of the flywheel momentum for the compression of the mixture(air and fuel) and at that same time the spark plug is fired for power known as the power stroke and when the mixture expands the piston moves down from the top dead center to the bottom dead center also the waste gas is been given off through the outlet valve. At the end of this stroke the piston must have made a rotation of 360<sup>o</sup>.


#### <center>How the 4 Stroke engine works</center>

As written above, it all happen in 4 strokes which are Intake or suction, Compression, power stroke and exhaust stroke. 

![U5duASUAVF5Ewy4HocJBBuV7jgbvoYX.gif](https://steemitimages.com/DQmdLWjMk6BC1Qb5js4BkAMWupnWfASFf1YB9rJ7QhVkaXD/U5duASUAVF5Ewy4HocJBBuV7jgbvoYX.gif)
<sub>[gif credit: Zephyris CC3.0 Licensed](https://en.m.wikipedia.org/wiki/User:Zephyris)</sub>

(1)  Suction Stroke: 
The suction stroke is the stages where the air and fuel enters the combustion chamber. For this to happen there is an inlet value as well as the outlet valve. It's starts by the opening of the inlet valve with the 180<sup>o</sup> rotation of the crankshaft, the piston moves from TDC to BDC (Top dead center to Bottom dead center) and also the outlet valve stays closed for the fuel and air to enter into the combustion chamber. 

(2)  Compression stroke: 
At this stroke the piston moves again from the bottom dead center to the top dead center with help of the momentum from the flywheel and the crankshaft completes a 360<sup>o</sup> rotation to compress the mixture (air and fuel) and for the compression to take place the inlet valve and outlet valve stays closed. 

(3)  Power stroke: 
The stroke is the part where power is been generated, the inlet and outlet valve remains closed, the piston rotates another 180<sup>o</sup> that makes a total rotation is 540<sup>o</sup>. The expansion of the mixture (air and fuel) is ignited with the help if the spark plug to produce a spark that produces the mechanical work. 

(4)  Exhaust stroke: 
The exhaust stroke is where the waste gotten from the combustion process is been pass out as waste gas. Here the outlet valve opens and the inlet valve closes with the help of the momentum from the flywheel in other to move the piston from bottom dead center to top dead center so as to move out the waste through the outlet valve which is the exhaust. For all that to happen the crankshaft makes another 180<sup>o</sup> rotation making a total of 720<sup>o</sup>.


### Conclusion 
Spark ignition engine and Compression ignition engines are aimed at producing mechanical work but works differently and obeys different principles, personally I would always pick the spark ignition for personal and commercial use unless I want to get a truck for heavy lifting then the compression ignition is much needed  and also with the explanation above about the 2 and 4 Stroke Engines I want to believe most of us thinking most automobile engines have the same principles have a better understanding now because they all have the same outcome does not mean they have the same mechanism like all generators produce power but some of them have 2 stroke engine and some 4 Stroke engine. 


</div>

### References for more information
<sub>[Comparison of Spark Ignition (SI) and Compression Ignition (CI) Engines](https://www.brighthubengineering.com/machine-design/1537-comparison-of-spark-ignition-si-and-compression-ignition-ci-engines/)</sub>
<sub>[ignition](https://www.google.com.ng/search?client=ms-android-transsion&ei=n-YDW-riEcLIgAbx8aKACw&q=ignition+meaning&oq=ignition+meaning&gs_l=mobile-gws-wiz-serp.3..0i67i70i249j0l4.3370.7496..10369...1....428.3665.3-8j2......0....1.........0i71j0i67j0i22i30j0i13i70i249j0i13.RWVQuWq43zQ%3D)</sub>
<sub>[Differences Between SI Engine and CI Engine](https://me-mechanicalengineering.com/differences-between-si-engine-and-ci-engine/amp/)</sub>
<sub>[spark ignition and Compression ignition difference](https://engineeringinsider.org/difference-si-engine-ci-engine/)</sub>
<sub>[Different Types of Engine](http://www.mechanicalbooster.com/2016/08/different-types-of-engine.html)</sub>
<sub>[How does 2 Stroke engine works](http://www.mechanicalbooster.com/2016/08/different-types-of-engine.html)</sub>
<sub>[How does the 4 Stroke engine works](http://mechstuff.com/how-does-a-4-stroke-engine-work)</sub>
<sub>[Internal combustion engine](https://en.m.wikipedia.org/wiki/Internal_combustion_engine)</sub>

![DQmPtnKZW6cQWBAzpA8yiqTDXSsVH9zEUyxFiek2kGEoA8g.gif](https://steemitimages.com/DQmPtnKZW6cQWBAzpA8yiqTDXSsVH9zEUyxFiek2kGEoA8g/DQmPtnKZW6cQWBAzpA8yiqTDXSsVH9zEUyxFiek2kGEoA8g.gif)

#### Thanks for your time 


<hr>
@osariemen