Two Stroke engine – Petrol and diesel

Two Stroke engine – Petrol and diesel. Guys, basically a stroke means the linear distance the piston moves between the top dead center (T.D.C)and the bottom dead center(B.D.C).so as the name suggest “2-stroke” means that the piston moves two times In between T.B.C and B.D.C. In other words we can say that a engine in which 2 strokes are carried out by the piston can be termed as a two stroke engine.

  • The basic concept of a two stroke engine is that all the essential operations are carried out in one revolution of crank shaft or two strokes of the piston.

Classification of two stroke engine

  • 2 stroke petrol engine
  • 2 stroke diesel engine

Basic components of a two stroke petrol engine

The figure shows all the components of petrol engine, with labels indicated.

Two Stroke engine – Petrol and diesel

Basic components of a two stroke diesel engine

The figure shows all the components of diesel engine, with labels indicated.

two Stroke engine – diesel

Difference between Two Stroke engine – Petrol and diesel

 


Petrol engine

Diesel engine
In a petrol engine we use spark plug for spark ignition While in the diesel engine we use fuel injector and thus accomplish a task of compression ignition
Petrol engine uses a carburetor the main
function of which is to properly mix the charge (air + fuel).
While there is no such facility in a diesel
engine
In petrol engine charge in the form of air +fuel In diesel engine the charge intake is only
in form of air
A petrol engine works on Otto cycle A diesel  engine works on diesel cycle
Operates on constant volume process Operates on constant pressure process
Uses gasoline as a fuel or petrol alternatively Uses diesel as fuel
Better efficiency for same compression
ratio
Low efficiency
Cheaper engine. Costlier engine
Less maintenance More maintenance
Easy to start due to lower
compression ratio
Difficult to start

 

Here is the Diagram showing Otto Cycle of Petrol Engine and Diesel Cycle of Diesel Engine:

Otto Cycle:

OTTO CYCLE : two Stroke engine – Petrol and diesel

Diesel Cycle:

DIESEL CYCLE – two Stroke engine – Petrol and diesel

General Working Of Two Stroke engine – Petrol and diesel

Two Stroke engine – Petrol and diesel
  • OPERATION-

In a two stroke engine,the inlet ,transfer and exhaust ports are covered and uncovered. By the movement of piston so according to the opening and closing of exhaust , inlet and transfer port following process es take place in a two stroke engine.

  • CHARGE TRANSFER AND SCAVENGING-

When the piston is nearer to the B.D.C,the transfer and exhaust port open up.the charge is slightly compressed due to which it enters the transport port and due to which it drives out the exhaust gases in the cylinder through the exhaust port.

IT CAN BE SEEN FROM THE DIAGRAM THAT  THE PISTON TOP IS MADE DEFLECTED IT IS BASICALLY DONE TO DEFLECT THE INCOMING CHARGE UPWARDS AND THUS SWEEPING OUT THE BURNT GASES.THIS PROCESS IS KNOWN AS “SCAVENGING”.

  • COMPRESSION AND SUCTION-

As the piston now moves upwards  the exhaust port and the transfer port are been closed and thus the charge is been trapped and the charge inside the cylinder is compressed.at the same time due to crank movement the suction poet opens and  due to the partial vacuum created due to compression ,the fresh charge is forced inside.

  • COMBUSTION-

As the piston reaches T.D.C a height intensity  spark  ignites the spark and thus start the combustion.due to this height pressure is generated inside the cylinder and it is forced downwards.at about 80% downward stroke the exhaust gases move out through the exhaust port.and now  the gases again enter the cylinder in form of new charge due to pressure difference this process is called “charging”.

These were the basic process that takes place in both diesel and the petrol engines,but in the diesel engine we use  fuel injector instead of spark plug.

SPARK PLUG – two Stroke engine – Petrol and diesel
FUEL INJECTOR – two Stroke engine – Petrol and diesel

Port timing diagram for  petrol engine

After studying the working we need to look at the port timing,which refers to the relative opening and closing of the ports with respective to the crank rotation.

PORT TIMING DIAGRAM
  • COMPARING TWO BRANDS - BRAND -A v/s BRAND-B

“What makes a racing engine so powerful and fast? Well it is the small details that make the difference. Probably, huge amounts of money invested in R&D; it’s not just on the engine design, but also on the manufacturing of the engine. Many racing engine manufacturers use special equipment to make their parts, like laser cutters and special high precision balancing equipment that your ordinary tool-and-die shop simply doesn’t have access to. The process control necessary to make a piston and sleeve assembly that will seal properly at high temperatures and last while being used in an engine capable of turning 30,000 RPM, is not easy. One single out of spec part could cause the engine to fail prematurely. Simple numbers like engine displacement and the color of the heat sink head are not going to tell you if the engine is any good or not. Even the manufacturer’s suggested HP has to be taken with a grain of salt. Engine “A” can crank out 1HP… under what conditions? What temperatures? How long? At what RPM? These are all blurry claims. It’s best to ask around your local track and choose a manufacturer with a history of good, reliable, and easy to tune engine designs. It’s always better to ask around than to waste your hard earned money on the flavor of the month engine manufacturer. Hey, with basic machining tools and a CAD model, anyone can make an engine. It takes years of experience and machine know-how to build a great engine! Make no mistake, some of the sport engines from the manufacturer “B” will burn the barn doors from the turbo model of brand “A”.”

Tips for better running of two stroke engines-

For smooth running of the engine we can use engines with less peak horse power.another method would be to adopt a suitable transmission system according to the needs.another implementation can be  by doing proper tuning  of pipe designs in order to help the 2 stroke engine.

Where are two-cycle engines used?

Two-cycle engines are inexpensive to build and operate when compared to four-cycle engines. They are lighter in weight and they can also produce a higher power-to-weight ratio. For these reasons, two-cycle engines are very useful in applications such as chainsaws, Weed-eaters, outboards, lawnmowers and motorcycles, to name just a few. Two-cycle engines are also easier to start in cold temperatures. Part of this may be due to their design and the lack of an oil sump. This is a reason why these engines are also commonly used in snowmobiles and snow blowers.

Some advantages and disadvantages of two-cycle engines

Because two-cycle engines can effectively double the number of power strokes per unit time when compared to four-cycle engines, power output is increased. However, it does not increase by a factor of two. The outputs of two-cycle engines range from only 20 to 60 percent above those of equivalent-size four-cycle units. This lower than expected increase is a result of the poorer than ideal charging efficiency, or in other words, incomplete filling of the cylinder volume with fresh fuel and air. There is also a major disadvantage in this power transfer scenario. The higher frequency of combustion events in the two-cycle engine results in higher average heat transfer rates from the hot burned gases to the motor’s combustion chamber walls. Higher temperatures and higher thermal stresses in the cylinder head (especially on the piston crown) result. Traditional two-cycle engines are also not highly efficient because a scavenging effect.

How are two-cycle engines lubricated?

Two-cycle motors are considered total-loss type lubricating systems. Because the crankcase is part of the intake process, it cannot act as an oil sump as is found on four-cycle engines. Lubricating traditional two-cycle engines is done by mixing the oil with the fuel. The oil is burned upon combustion of the air/fuel mixture. Direct Injection engines are different because the fuel is directly injected into the combustion chamber while the oil is injected directly into the crankcase. This process is efficient because the fuel is injected after the exhaust port closes, and therefore more complete combustion of fuel occurs and more power is developed. Direct injection engines have a higher power density than traditional two-cycle engines. Because the oil is directly injected into the crankcase, less oil is necessary and lower oil consumption results (80:1 range). Direct Injection motors have higher combustion temperatures, often up to 120F. They also require more lubricity than traditional two-cycle motors.

I HOPE THAT THROUGH MY ARTICLE YOU ALL MIGHT HAVE GOT A BRIEF OVERVIEW ABOUT THE TWO STROKE ENGINES…..! STAY TUNED FOR MORE SUCH AUTOMOBILE TOPICS…! IN MY NEXT ARTICLE I WILL TRY TO COVER AS MUCH AS I COULD, REGARDING THE APPLICATIONS OF TWO STROKE ENGINES,NITRO ENGINES,AND I WOULD CERTAINLY GIVE SPECIFICATIONS REGARDING THE BIKES AND ATV’S USING 2-STROKE ENGINE.

SUGGESTIONS AND COMPLIMENTS ARE ALWAYS WELCOMED…!

  • ADITYA  KAPSE

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