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Understanding two-stroke diesel and gasoline engines

Two-stroke, which is known as the two-cycle engines are types of internal combustion engines that works differently from four-stroke engines. In this situation, it takes two-stroke to completes a power cycle. That is, the upward and downward movements of the piston are one revolution of the crankshaft. The dissimilarity with the four-stroke engine is that it takes four strokes of the piston to complete a power cycle during two crankshaft revolutions.

The surprising truth about the two-stroke engine is that the beginning of the compression stroke and the end of the combustion stroke occur simultaneously. Meanwhile, the intake and the exhaust take place at the same time. Comparing to four-stroke engines, two-stroke engines always have a high power-to-weight ratio, that is, power accessible in a narrow range of rotational speeds, known as the “power band”. It has a greatly decreased number of moving parts making it portable and more effective.

Today you’ll learn the definition, diagram, history, and working of two-stroke engines. You’ll learn how they work on both diesel and gasoline engines.

Read more: Understanding four-stroke engines

Two-stroke diesel and gasoline engines

Small gasoline-powered two-stroke engines recognized as crankcase-compression engines. They are lubricated by a petrol mixture in a total-loss system. The oil mixed at a preceding time with the petrol fuel, in a ratio of about 1:50. The oil forms emissions as oily droplets in the exhaust or by being seared.  This helps to produce extra exhaust emissions with extreme hydrocarbons, than four-stroke engines of equal power output. Due to the equal opening time of the intake and exhaust ports in some two-stroke engine designs. Some amount of unburned fuel gases are allowed to leave the exhaust stream. However, small air-cooled engines with high combustion temperatures may give high NOx emissions.

Read more: Difference between 2 stroke and 4 stroke engines

diagram of Two-stroke petrol engines

Two-stroke diesel engines entirely depend on the heat of compression in order to ignite. A uniflow diesel engine receives air to the chamber, and the exhaust gases leave through an overhead poppet valve.
In the case of Schnuerle ported and loop-scavenged engines, intake and exhaust take place through piston-controlled ports. All two-stroke diesel are scavenged by forced induction. Though some designs use a mechanically driven roots blower, whilst marine diesel normally uses exhaust-driven turbochargers, using electrically driven auxiliary blowers for low-speed operation when turbochargers are unable to deliver enough air.

Read more: Understanding diesel engine

A propeller is directly fitted to a marine two-stroke diesel engine, making it run in both directions. The valve timing and fuel injection are mechanically readjusted by using a different set of cams on the camshaft.

diagram of Two-stroke diesel engines

Read more: Understanding petrol engine

Watch the video below to learn the working of two-stroke engines on gasoline and diesel engine:

Modern two-stroke engines are designed with a power valve system. They are fitted manually in or around the exhaust ports. The working of these valves is as follows:
The exhaust port is transformed by closing off the top part of the port, which alters the timing. Or by altering the quantity of exhaust, which changes the vibrant frequency of the expansion chamber.

Read more: Things you need to know about car sensors

One of the greatest advantages of two-stroke engines is direct injection. It helps in abolishing some pollution and waste produce by the carbureted two-stroke; the amount of fuel/air mixture penetrating the cylinder instantly goes out unburned through the exhaust port.
The two systems use are low-pressure air-assisted injection and high-pressure injection.


The first commercial 2stroke engine was credited to Dugald Clerk, a Scottish engineer who patented his plan in 1881. The clerk design was totally distinct, having a separate charging cylinder. Englishman Joseph Day was also credited for the crankcase-scavenged engine for using an expanse below the piston as a charging pump. A popular German inventor, Karl Benz produced a two-stroke engine on 31 December 1879, which he gained copyright In 1880.
The first confirmed two-stroke engine was attributed to a man who started producing twin-cylinder water-cooled motorcycles in 1908. His name is Yorkshireman Alfred Angas Scott.

Read more: Difference between petrol and diesel engine

That is all for this article, where the definition, diagram, and working of two-stroke engines are being explained for both gasoline and diesel engines. I hope you enjoyed the reading, if so, kindly share with other students. Thanks for reading, see you next time!

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