15:1
The ideal (theoretical) air-fuel ratio, for a complete combustion, is called stoichiometric air-fuel ratio. For a gasoline (petrol) engine, the stoichiometric air-fuel ratio is around 14.7:1. This means that, in order to burn completely 1 kg of fuel, we need 14.7 kg of air.
beginning of suction stroke
The answer is much obvious because the suction stroke happens just after the exhaust stroke when all the hot exhaust gases are scavenged out off the cylinder. Then in suction stroke through intake manifold the cool and fresh air fuel mixture is drawn inside the cylinder, which decrease the temperature inside the cylinder and this way the temperature would be minimum at the beginning of the suction stroke.
75 to 90 %
The volumetric efficiency of a well designed engine may be between 75 to 90 %.
critically damped
If the damping factor for a vibrating system is zero, then the system will be undamped.
If the damping factor for a vibrating system less than one and greater than zero, then the system will be under damped.
If the damping factor for a vibrating system is unity, then the system will be critically damped.
If the damping factor for a vibrating system is more than unity, then the system will be over damped.
transverse vibration
A reed type tachometer use the principle of transverse vibration.