Understanding two-stroke diesel and gasoline engines

Two-stroke, which are known as two-cycle engines are types of internal combustion engines that work differently from four-stroke engines. In this situation, it takes two strokes to complete 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. Compared 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 workings of two-stroke engines. You’ll learn how they work on both diesel and gasoline engines.


Two-stroke diesel and gasoline engines

Small gasoline-powered two-stroke engines are recognized as crankcase-compression engines. They are lubricated by a petrol mixture in a total-loss system. The oil is 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.

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, marine diesel normally uses exhaust-driven turbochargers, using electrically driven auxiliary blowers for low-speed operation when turbochargers are unable to deliver enough air. 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: Difference between 2-stroke and 4-stroke engines

Watch the videos below to learn the workings of two-stroke engines on gasoline and diesel engines:

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.

One of the greatest advantages of two-stroke engines is direct injection. It helps in abolishing some pollution and waste produced 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 used are low-pressure air-assisted injection and high-pressure injection.

Read more: Applications, Pros, and Cons of Two-Stroke Engines


The first commercial 2-stroke engine was credited to Dugald Clerk, a Scottish engineer who patented his plan in 1881. The clerk’s 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.

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

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