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PROS. A secondary cylinder provides an additional expansion process enabling extra work to be extracted, which results in better thermodynamic efficiency (which means less thermal energy is wasted, hence the engine efficiency must increase) 5 stroke engines tend to be quite small as the firing (smaller) cylinders can be very highly rated.
Bore is the diameter of each cylinder and stroke is the length that it travels when moving from bottom position to the top position. Thus if the engine has 1 cylinder with bore x stroke of 78 x 52.3 mm it's total displacement will be: where π = 3.1416... and the bore and stroke must be in cm, thus divide them by 10 to get the right dimension.
Question 2: As @Paulster2 says, we're talking about a 4-stroke engine, so you have 2 TDC positions, only one of which has a combustion event. The exhaust valve opens at BDC and stays open during the exhaust stroke, and potentially stays open until the start of the intake stroke. So no problems there.
A popular explanation of how a four stroke engine works is Suck, squeeze, bang, blow. The engine sucks in a mixture of fuel and air, then squeezes it together (compresses it), then it burns / explodes that with a bang , and finally it blows out the exhaust.
As you rock the crank back and forth, the set of pushrods that move alternately up and down are the cylinder that is "rocking" or just finished the exhaust stroke and commencing the inlet stroke. The set of pushrods that don't move are the cylinder that is about to fire, commencing the power stroke.
That means in a four stroke engine the shaft rotates twice (two revolutions) for every four stroke cycle, which means one power stoke for every two revolutions of the crank. So, if the crank is turning 1000 times per minute, that would be 500 power strokes (firing of the spark plug) on each cylinder in that one minute.
In many ways, you're describing a 5 stroke engine. 5 Stroke engines are using a piston to provide a secondary means of compression for the AFR. Although, not injecting air they are compressing the air by mechanical means. What you describe with air injection requires massive volumes of air. Think of a 5.0 Liter engine requiring 5 liters air ...
How much fuel do various types of engines burn per power output? I'm especially interested in naturally aspirated piston engines, and comparing two-stroke to four-stroke. The wikipedia article gives the value for several specific engines, but they're mostly for either aircraft or marine applications.
9. With regular driving the Air/Fuel ratio is kept constant at 14.7:1. So if a larger engine needs more air (more swept volume) per cycle then yes it will require more fuel. So the question boils down to which engine has more friction per cycle, and which car has more weight to carry around.
For small gasoline engines, the two stroke engine is a cost and weight saving method. Since the two stroke engine has a combustion cycle twice as often, so for the same displacement, it has twice as much power. Therefore, an engine of a given power costs and weighs less. Furthermore, the reduction in moving parts results in more cost saving.