Fuel Types, Properties, Combustion, and Lubrication

Posted on Mar 14, 2025 in Chemistry

Fuel Types

  • Solid
    • Natural
    • Artificial
  • Liquid
    • Alcohols
    • Waste
    • Derived from petroleum
  • Gaseous
    • Waste
    • Natural gas
    • Liquefied Gases
    • Artificial
    • Biogas

Properties of Fuels

  • Density: The amount of mass per unit volume, measured in kg/dm3.
  • Viscosity: The physical measurement of the resistance of a liquid to flow when an external force is applied.
  • Kinematic viscosity: The ratio of absolute viscosity and density, both measured at the same temperature.
  • Calorific Value (for liquid fuel): Indicates the amount of heat released when undergoing a combustion process. The product is in its final state of oxidation, reflecting the potentially available thermal energy.
  • Flash Point (of a liquid fuel): Indicates the temperature at which the fuel emits enough vapor, caused by warming, so that it can be ignited by a pilot flame.
  • Cloud Point (specified for diesel fuel): The temperature, expressed in intervals of 1°C, at which the first crystals of paraffin appear in a sample in a container when cooled under certain prescribed conditions.
  • Cold Filter Plugging Point (CFPP): Gives an indication of the lowest temperature at which the fuel can pass through a filter.
  • Aniline Point: The minimum temperature at which a mixture of equal parts by volume of aniline and the product to be tested is miscible. Aniline is an aromatic substance.
  • Specific Heat: Defined as the amount of heat that must be applied to a unit mass to increase its temperature by one degree. It is usually expressed in kcal/kg °C.
  • Thermal Conductivity: The amount of heat per unit time.
  • Freezing Point: The lowest temperature at which the fuel still flows.
  • Diesel Index: A number that measures the ignition power of a fuel.

Lubricating Oils

Lubricating oils used in engine lubrication are composed of various hydrocarbons of mineral origin and are obtained by distillation of petroleum. Additives are compounds that enhance the quality of pure mineral oil.

  • Antioxidants: Reduce the tendency to oxidation in contact with air.
  • Anticorrosives: Neutralize acids that attack the metal parts in contact with the oil.
  • Detergents: Clean the ducts and prevent solid waste, sludge, and varnish.
  • Dispersants: Avoid the crowding of substances, keeping them in suspension.

Oil Classification

Oils are classified by their viscosity and conditions of use:

  • Viscosity is classified by SAE, which relates viscosity to temperature.
  • Their use is given by the API, based on their quality and type of service operation.

Combustion

Combustion is an exothermic chemical reaction; the combination of fuel and a certain temperature, with oxygen in the air. The combustion process is rapid oxidation during which energy is released as light and heat instantly.

  • Elements involved in combustion: Fuel and Oxidizer

Reducing Noise from Diesel Engines

  • Use of fuels with a high cetane index.
  • Improved air turbulence.
  • Reduction of the amount of fuel under the action of the initial power.

Abnormal Combustion in Engines

  • Self-ignition: Occurs in the compression period and does not require a spark, but occurs because of the temperature.
  • Detonation: Occurs in the late stage of combustion; it is the burning of leftover combustion products.
  • Knocking: The abnormal increase in pressure which causes the self-ignition of the mixture.

Diesel knocking is caused by the advancement of the injection.