Here’s a breakdown of each term related to diesel fuel:
(a) Cetane Number:
The cetane number is a critical indicator of a diesel fuel’s ignition quality. It represents the delay between fuel injection and the start of combustion in a diesel engine. Here’s a breakdown:
- Higher Cetane Number: Indicates a shorter ignition delay. This is ideal for smooth engine operation, minimizing knocking and incomplete combustion.
- Lower Cetane Number: Represents a longer ignition delay. This can lead to rough engine operation, increased noise (knocking), and incomplete combustion resulting in higher emissions.
Cetane number is similar to the octane rating used for gasoline, but they measure different properties.
(b) Calorific Value:
The calorific value, also known as heating value, refers to the amount of heat energy released when a unit mass of fuel is burned completely. It’s typically expressed in units like Megajoules per kilogram (MJ/kg) or British thermal units per pound (Btu/lb).
A higher calorific value indicates the fuel contains more potential energy per unit mass. This translates to more power output from the engine for a given amount of fuel burned.
(c) Density:
Density refers to the mass of a fuel per unit volume. It’s typically expressed in kilograms per liter (kg/L) or pounds per gallon (lb/gal).
Density is important for several reasons:
- Fuel Economy: Denser fuels store more energy per unit volume, potentially leading to better fuel economy (assuming similar calorific values).
- Injection Systems: Fuel injection systems are calibrated for a specific fuel density. Significant deviations can affect engine performance.
(d) Viscosity:
Viscosity refers to a fluid’s resistance to flow. In the context of diesel fuel, it describes how easily the fuel flows at a given temperature. It’s typically measured in units like centiStokes (cSt).
Here’s how viscosity affects diesel engines:
- Cold Starts: At lower temperatures, higher viscosity can make it harder for the fuel to flow, hindering engine starting.
- Injection and Atomization: Proper fuel atomization (breaking down into fine droplets) is crucial for efficient combustion. High viscosity can hinder this process.
Pump Wear: Fuel pumps rely on the fuel’s lubricating properties. Very low viscosity can increase wear on pump components.