What is a lubricant?
Is a substance, usually organic, introduced to reduce friction between surfaces.
What properties must a lubricant possess?
- A high boiling point and low freezing point (in order to stay a liquid over a wide range of temperatures.
- High viscosity index.
- Thermal stability.
- Hydraulic stability.
- High resistance to oxidation.
- Corrosion prevention.
What are lubricants composed of?
Typically contain 90% base oil (mineral oils) and less than 10% additives. Group 1 - 5.
Give a few examples of base oil.
Vegetable oils such as esters, silicones and fluorocarbons. Can be synthetic or minerals.
What do additives do?
Increase viscosity, improve viscosity index, have resistance to corrosion/oxidation. They all have a life span.
How many additives are contained within lubricants?
As many as 10 additives.
Give a few examples of additives.
- Antifoaming agents which lower surface tension in order to discourage foam formation.
- Viscosity index improvers (VIIs) allowing lubricants to remain viscous at higher temperatures. This also means high resistance (thick).
- Antioxidants: suppress the rate of oxidative degradation of the hydrocarbon within the lubricant.
- Corrosion inhibitors, usually alkaline materials.
- Anti-scuffing additives against extreme pressures.
Name 5 types of lubricants.
- Mineral oils, derived from crude oil.
- Synthetic oils, produced from synthetic hydrocarbons.
- Solid lubricants, including PTFE, inorganic solids such as graphite, metal alloys used as grease additives.
- Aqueous lubrication, PEG which are strongly hydrated brush polymers.
- Bio Lubricants, derived from vegetable oils and other renewable sources.
How does a lubricant transfer heat?
Both gas and liquid lubricants can transfer heat. Liquid lubricants are much more effective because of their high specific heat capacity. The liquid is constantly circulated to and from a cooler part of the system. The drawback is when a system suddenly shuts down, the oil can immediately oxidise and clog the oil ways.
Disposal and environmental impact of lubricants.
40% of lubricants are released into the environment. Recycled, burned or disposed into landfill waste. Regulations in place for a threshold level of lubricant that may be present in waste streams. Burning generates airborne pollution and toxic materials, mainly heavy metal compounds. Landfill sites handle the toxic ash and specialised facilities handle airborne pollution. Other disposal methods include run-off from roadways, accidental spillage or natural disasters. The additives added to lubricants are considered to be toxic and can be harmful to the environment.
What is the calorific value of fuel?
It is the total quantity of heat liberated when a unit mass/volume of fuel is completely burnt.
What is higher calorific value (HCV)?
It is the total amount of heat produced when a unit of mass/volume has been completely burnt and the products of combustion have been cooled to room temperature.
What is lower calorific value (LCV)?
It is the heat produced when a unit of mass/volume of fuel is burnt completely and the products are permitted to escape.
Where are natural/primary fuels found?
In nature, such as wood, peat, coal, natural gas and petroleum.
Properties of an ideal fuel.
- High calorific value.
- Moderate ignition temperature.
- Low moisture content.
- Easy to transport.
- Combustion must be controlled.
- Should burn in air.
- Low cost.
Explain thermal efficiency
Measure of thermal energy such as an internal combustion engine. It is the fraction of energy added by heat that is converted to net work output (performance).
How to improve internal combustion engine efficiency?
- Turbochargers, is an exhaust gas recovery device that increases boost air pressure thereby optimizing combustion. It increases efficiency by 7-8%.
- Using the correct viscosity of lubricating oil, as visocosity is linked to friction.
- Direct fuel injection, increasing efficiency by 11-13%.
What is heat?
Heat is a form of energy that affects the temperature of objects by changing movement of atoms/molecules.
What is fuel?
Fuel is a combustible substance, containing carbon as a main constituent, gives large amount of heat and work upon burning.
Secondary fuels?
Prepared fuels such as kerosene, diesel, petrol, bio-gas, natural gas, water gas, charcoal, coke.
Ignition temperature?
The lowest temperature at which the fuel starts burning smoothly. Gases - Low, Solid - High.
Non-combustible matter:
Does not take part in combustion process, it remains in the form of ash, and it also reduces the heating value.
Synthetic oil vs. Mineral oils
- Mineral oil is a petroleum product from the ground, whereas synthetic oils are made in controlled environment to get a uniformed product.
- Mineral oils come as different sizes whereas as synthetic oil consists of the same sized particles.
What things are to be considered with oil?
- Thickness.
- Size matter (particles) of lubricant.
- Viscosity.
- Flash point.
- Oiliness.
