2 Stroke Vs. 4 Stroke Outboard Motors Show Posted in Wednesday, May 25, 2022 What is the difference between a 2-stroke and 4-stroke outboard motor? As the question points out, one main difference is the number of movements (strokes) it takes for the piston to complete a cycle. For example, a cycle on a 4-stroke engine begins with air and fuel intake to the compression stroke, where ignition of fuel and air occurs. So far, that is just two strokes. The third stroke brings the piston back to the bottom, and the fourth stroke presses out the exhaust as it raises to the top. That’s four strokes. The Two-Stroke Outboard CycleA two-stroke outboard requires only two piston movements to complete a cycle. Whereas in a 4-stroke outboard engine, the fuel and air enter at the top of the engine, a two-stroke engine allows fuel to enter the bottom of the piston housing. As the piston turns, the fuel and air are compressed and then ignited in one stroke. On the downstroke, an exhaust valve opens near the bottom of the combustion chamber, and as the piston continues its cycle, it forces gas and air into the combustion chamber, which forces out the exhaust. So the first difference is the mechanical design of both engines. One advantage of a 2-stroke engine is that it weighs less than a comparable 4-stroke outboard motor. That is because there are fewer moving parts in a 2-stroke engine than inside a 4-stroke engine. A con of 2-stroke engines is an increase in pollution and often an increase in fuel consumption. That is because of how the ignition and exhaust strokes work on a 2-stroke engine. As fresh fuel and air fill the combustion chamber, the exhaust exits via the exhaust valve. Along with the exhaust is some unburned fuel. That is a fundamental problem with 2-stroke engines, though new advancements in marine engine tech are changing thanks to direct fuel injection and sometimes the inclusion of a catalytic converter. Stricter environmental regulations nearly killed off the 2-stroke engine because of significant hydrocarbon emissions from 2-stroke boat motors. The Engine Oil IssueWith a 2-stroke engine, the oil supplied to the engine’s moving parts can be handled in two ways.
Interestingly enough, once the oil is in the gas and the gas is in the fuel tank, the engine has oil. This is because an oil injection system pushes a specific amount of oil into the engine. If that part fails, the engine is without oil, which often means a catastrophic engine event. Pros and Cons of 2-stroke and 4-stroke Outboard MotorsWe have gone over some pros and cons of both engines, but here we go:
Conclusion — 2-stroke vs. 4-stroke marine enginesMany new marine engines are 4-stroke because they offer better emission ratings over older 2-stroke boat motors. That, however, is not a universal truth, rather a generalization in the evolution of boat motors. Many physical engine changes occur due to regulations at the state level, which also vary from one state to the next. These regulations have created an opportunity for anglers with 4-stroke engines to fish or boat in places where anglers or boaters with 2-stroke engines are no longer permitted. Is one engine better than the other? It is a highly subjective answer, and much of how you answer that question comes down to how you use your boat, where you want to boat, and how diligent you are with outboard motor maintenance. There are as many positives for each motor as there are negatives. One gets better fuel economy but is 30-50 percent heavier. One is not very environmental but is lighter and easier to maintain. The list continues. Should you buy a 2-stroke motor for your boat? Should you opt for the 4-stroke engine instead? Personally, a 4-stroke makes more sense if you are an angler. A healthier environment means better fishing opportunities. If you want to go farther on a tank of gas, then the 4-stroke is a good choice as it has better fuel economy. If lifting a heavy boat motor is not for you, a 2-stroke is an option, and you can find certain brands of 2-stroke boat motors with excellent emission standards. Why 2A two-stroke engine can burn low-grade fuel oil and hence reduce the running cost of the ship.
What is 4A 4 stroke engine can be installed on the ship to produce electrical power and also to propel the ship (usually in small size vessel). This engine takes 4 cycles to complete the transfer of power from the combustion chamber to the crankshaft.
What is constructional difference between 2A 4 stroke engine completes 2 rotations of the crankshaft after finishing one cycle, where a 2 stroke engine completes only 1. With a 4 stroke engine, power is produced once every 4 strokes of the piston whilst power is produced every 2 strokes in a 2 stroke engine.
Do ships use 4Most modern larger merchant ships use either slow speed, two stroke, crosshead engines, or medium speed, four stroke, trunk engines. Some smaller vessels may use high speed diesel engines.
|