ZEV or Zero Emission Vehicle: A vehicle not emitting any pollutants through exhaust, is called ZEV or Zero Emission Vehicle. As at present only electric vehicles and some fuel cell vehicles may be rightly called ZEV.

Zener diode: A special type of diode that acts as ordinary diode upon a certain voltage called the breakdown voltage above which it allows the reverse-bias current to flow. It is used in control circuit, such as to regulate field current in an alternator.

Wheel motor: An electric motor which is installed into a wheel and drives it directly.

Water jacket: Passage around the engine cylinder for the circulation of coolant. These arc cast as integral parts of the cylinder block and head.

Wankel engine: A rotary engine working on Otto cycle.

Volumetric Efficiency: Volumetric Efficiency of an engine is the ratio of the volume of the air actually inducted in a given time at the atmospheric conditions surrounding the engine, to the total piston displacement or swept volume of the engine.

Viscosity: Resistance of a fluid to flow; most important property of a lubricating oil.

Venturi: A restriction in the entrance passage of a carburettor where the main fuel jet is placed.

Variable Timing Electronic Control (VTEC): Honda's variable valve timing system controlled electronically.

Variable Length Intake Manifold (VLIM): An automobile engine manifold technology, which can vary the length of the intake tract to optimize power and torque as well as to improve fuel efficiency. Also called VRIS (Variable Resonance Induction System). It has two main effects: 1. Swirl, which helps form a homogeneous air-fuel mixture which ignites without detonation. At low engine speeds, air is directed through a longer path with limited capacity, increasing the speed of an flow. At higher loads, shorter and higher capacity path opens to increase the amount of air flow. 2. Pressurization by means of a tuned intake…

Valve train: The system which operates intake and exhaust valves, consisting of camshaft(s), valves springs, lifters, push rods and rocker arms.

Valve overlap: The duration when both the inlet and the exhaust valves are open simultaneously, in terms of degrees of crankshaft rotation.

Undersquare engine: An engine with the stroke to bore ratio more than one.

Ultra Low Emission Vehicle (ULEV): A vehicle which emits emission less than the limits specified by the California Air Resource Board. U.S.A.

Turbulence: A type of flow in which randomly dispersed vortices of different sizes become superimposed into the charge (air or air-fuel mixture) flow stream. These vortices are carried along with the flow stream and form breakaways having concentric spiral motion. The whirling of these vortices causes interaction with adjacent vortices, increasing the fuel mixing and heat transfer rate.