2- stroke engine

Steam Locomotive Engine.

Steam Locomotive Engine

Steam engines powered most trains from the early 1800s to the 1950s.¹ Though the engines varied in size and complexity, their fundamental operation remained essentially as illustrated here.

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In a steam engine, the boiler (fueled by wood, oil, or coal) continuously boils water in an enclosed chamber, creating high-pressure steam.

First stroke

Steam from the boiler enters the steam chest and is admitted to the front end of the cylinder by a valve slide (illustrated in blue). The high pressure steam presses the piston backward, driving the engine wheels around one half turn.

Exhaust

At the end of the piston stroke, the valve shifts, allowing the remaining steam pressure to escape through the exhaust port underneath valve slide (in blue). The pressure escapes in a quick burst which gives the engine its characteristic choo choo sound.

Second stroke

At the same time, the valve slide begins admitting high pressure steam to the back end of the cylinder. This presses the piston forward, pulling the engine wheels around another half turn.

Exhaust

At the end of the second stroke, the steam is released from the rear portion of the cylinder (another choo).

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The steam engine has a dead spot at the extreme end of each stroke while the valve is transitioning from power to exhaust. For this reason, most engines had a cylinder on each side of the engine, arranged 90 degrees out of phase, so the engine could start from any position. This illustration only shows one side of the engine.

Although these illustrations are not scale represenations of any particular engine, they draw heavily from the many excellent illustrations in Modern Locomotive Construction.

Atkinson Engine-its working

Atkinson Engine

The Atkinson engine is essentially an Otto four stroke engine with a different means of linking the piston to the crankshaft.

 

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The clever arrangement of levers allows the Atkinson engine to cycle the piston through all four strokes in only one revolution of the main crankshaft, and allows the strokes to be different lengths.

The design eliminates the need for a separate cam shaft. The intake (if used), exhaust, and ignition cams are located on the main crank shaft. My illustration shows only an exhaust cam.

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Deviation from proper Atkinson cycle

Since this page was first published, I’ve learned a great deal about the Atkinson engine. Visitors to this site originally clued me in, which prompted me to do a bit more reading.

This illustration closely follows the dimensions of a model engine, described in the excellent book: Building the Atkinson Cycle Engine. In this design, the intake and exhaust strokes appear to be longer than the compression and power strokes. It’s not clear whether this was intentional; I suspect that the model designer was more interested in the linkage than the thermal cycle.

In a true Atkinson cycle, the power and exhaust strokes are longer than the intake and compression strokes.⁸By starting with a small initial charge, and allowing it to expand to a larger volume than it originally occupied, a greater degree of fuel efficiency is realized.

Atkinson designed more than one engine to capitalize on this important property. I hope to have better animations of them all some day.

For more on the Atkinson and all internal combustion engines, I highly recommend Lyle Cummins’ Internal Fire.

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Toyota Prius and the Atkinson cycle

A number of visitors have arrived at this page after reading somewhere that Toyota’s popular hybrid car, thePrius, uses an Atkinson cycle engine. I do not know where this claim originated, but I doubt that the Prius engine uses the linkage illustrated above.

It is possible to create the same effect as the Atkinson cycle by changing the valve timing on an otherwise ordinary Otto four stroke engine. I really should illustrate this, but in the meantime I hope the following explanation will suffice:

A cam is employed on both intake and exhaust valves (unlike my four stroke illustration). The intake valve cam is designed to hold the intake valve open for more than a single stroke:

• The intake stroke begins as usual, initially drawing a full cylinder of fuel-air mixture.
• When the piston begins its upward travel, the intake valve remains open. The piston pumps some of the fresh fuel mixture back out the intake port. The net effect is exactly the same as if the intake stroke were shortened.
• The intake valve closes after the piston has moved some predetermined portion of this stroke. Compression does not actually begin until this point, effectively shortening the compression stroke to match the shortened intake stroke.
• The power and exhaust strokes remain as in the four stroke, employing almost the entire length of the piston travel.

It’s possible that this is the way the Prius engine works, but I do not have an authoritative reference. The Toyota website does say that the Prius uses VVT-i or Variable Valve Timing with Intelligence⁹. This technology is probably related.

I would be grateful for a good, authoritative, reference on this subject. Can you direct me to it?

Wankel Engine-its working.

Wankel Engine

The Wankel rotary engine is a fascinating beast that features a very clever rearrangement of the four elements of the Otto cycle. It was developed by Felix Wankel in the 1950s.¹

 

Speed 10 fps

In the Wankel, a triangular rotor incorporating a central ring gear is driven around a fixed pinion within an oblong chamber.

Intake

The fuel/air mixture is drawn in the intake port during this phase of the rotation.

Compression

The mixture is compressed here.

Power

The mixture burns here, driving the rotor around.

Exhaust

And the exhaust is expelled here.

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The rotary motion is transferred to the drive shaft by an eccentric wheel (illustrated in blue) that rides in a matching bearing in the rotor. The drive shaft rotates once during every power stroke instead of twice as in the Otto cycle.

The Wankel promised higher power output with fewer moving parts than the Otto cycle engine; however, technical difficulties interfered with widespread adoption. In spite of valiant efforts by Mazda, the four stroke engine remains much more popular.

How diesel fuel injector works? And how nozzle spray ??.flv

Two Stroke Engine

Two Stroke Engine

 

The two stroke engine employs both the crankcase and the cylinder to achieve all the elements of the Otto cycle in only two strokes of the piston.

Intake

The fuel/air mixture is first drawn into the crankcase by the vacuum that is created during the upward stroke of the piston. The illustrated engine features a poppet intake valve; however, many engines use a rotary value incorporated into the crankshaft.

Crankcase compression

During the downward stroke, the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke.

Transfer/Exhaust

Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well.

Compression

The piston then rises, driven by flywheel momentum, and compresses the fuel mixture. (At the same time, another intake stroke is happening beneath the piston).

Power

At the top of the stroke, the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle. (At the same time, another crankcase compression stroke is happening beneath the piston.)

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Since the two stroke engine fires on every revolution of the crankshaft, a two stroke engine is usually more powerful than a four stroke engine of equivalent size. This, coupled with their lighter, simpler construction, makes the two stroke engine popular in chainsaws, line trimmers, outboard motors, snowmobiles, jet-skis, light motorcycles, and model airplanes.

Unfortunately, most two stroke engines are inefficient and are terrible polluters due to the amount of unspent fuel that escapes through the exhaust port.

2 Stroke Engine Animation

 Internal combustion engine 2 stroke.