Carbon and Fossil Fuels

Cooking oil or Vegetable oil can be used as an alternative fuel in diesel engines and in heating oil burners. When vegetable oil is used directly as a fuel, in either modified or unmodified equipment, it is referred to as straight vegetable oil (SVO) or pure plant oil (PPO). Conventional diesel engines can be modified to help ensure that the viscosity of the vegetable oil is low enough to allow proper atomization of the fuel. This prevents incomplete combustion, which would damage the engine by causing a build-up of carbon. Straight vegetable oil can also be blended with conventional diesel or processed into biodiesel or bioliquids for use under a wider range of conditions.

Hence, the correct option is $D$

Biomass is an organic material that comes from plants and animals and it is a renewable source of energy.

$\Rightarrow$  Bio-fuels are designed to replace gasoline, diesel fuel and coal, which are called “fossil fuels” because they are made from animals and plants that died millions of years ago. 

Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), also referred to as simply propane or butane, are flammable mixtures of hydrocarbon gases used as fuel in heating appliances, cooking equipment, and vehicles. The percentage of butane is around 70% and that of propane is around 30%.

Liquefied petroleum gas or liquid petroleum gas (LPG or LP gas), also referred to as simply propane or butane, are flammable mixtures of hydrocarbon gases used as fuel in heating appliances, cooking equipment, and vehicles. The percentage of butane is around 70% and that of propane is around 30%.

Sewer gases may include hydrogen sulphide, ammonia, $CO,SO _2,NO$, etc. Improper disposal of petroleum products such as gasoline and mineral gas spirits contribute to sewer gas hazards.

Hydrogen is both powerful and efficient. It is enough to provide power for powerful machines such as spaceships. Also, it is environmentally friendly and is a much safer choice compared to other fuel sources. Hydrogen is three times as powerful as gasoline and other fossil fuels. This means that it can accomplish more with less.

Petroleum and natural gas are formed by the anaerobic decomposition of remains of organisms including phytoplankton and zooplankton that settled to the sea (or lake) bottom in large quantities under anoxic conditions, millions of years ago. Over geological time, this organic matter, mixed with mud, got buried under heavy layers of sediment. The resulting high levels of heat and pressure caused the organic matter to chemically alter, first into a waxy material known as kerogen which is found in oil shales, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis. Despite these heat driven transformations (which may increase the energy density compared to typical organic matter), the embedded energy is still photosynthetic in origin.

There is a wide range of organic, or hydrocarbon, compounds in any given fuel mixture. The specific mixture of hydrocarbons gives a fuel its characteristic properties, such as boiling point, melting point, density, viscosity, etc. Some fuels like natural gas, for instance, contain only very low boiling, gaseous components. Others such as gasoline or diesel contain much higher boiling components.

Otto cycle is the typical cycle for most of the cars internal combustion engines that work using gasoline as a fuel. To reduce pollution LPG is used as a source of clean fuel. Blast furnace gas may be combined with natural gas or coke oven gas before combustion. Hence all of the above are used for internal combustion of engines.

Compressed natural gas (CNG) can now be used as a fuel for gas-fueled captive power plants. Natural gas as fuel source has a significant number of benefits versus diesel including reduced emissions and reduced fuel costs.

Natural gas can be used to generate electricity in a variety of ways. The most basic natural gas-fired electric generation consists of a steam generation unit, where fossil fuels are burned in a boiler to heat water and produce steam that then turns a turbine to generate electricity. It is a non-renewable resource. Natural gas is found in deep underground rock formations or associated with other hydrocarbon reservoirs in coal beds and as methane clathrates. Petroleum is another resource and fossil fuel found in close proximity to and with natural gas.

Compressed Natural Gas happens to be a very viable alternative to traditional fuels particularly for use in the automobile industry. Being low in pollutants, high in calorific value and heat yield, economical and available in abundance globally, CNG is the perfect alternative for most.

Secondly, CNG is environment friendly as it reduces vehicular exhaust emissions significantly. Carbon Monoxide emissions are reduced to a maximum of 90 per cent and Hydrocarbon emissions by 60 per cent as compared to vehicles that use Petrol. Carbon Dioxide emissions, a cause for global warming, are also reduced significantly by 10 per cent.

Non-luminous flames are the ones that burn blue. These flames have access to as much oxygen as they could possibly use, so they can burn very efficiently. All of the carbon that gets used can be turned into carbon dioxide, so there's actually no soot. Complete combustion of LPG takes place. Hence, it burns with a blue flame.

Liquefied Petroleum Gas is considered as cleanest fuel because of the following reasons:

1. LPG has a high calorific value. The calorific value of LPG is about 50 KJ/g.
2. It is very neat and clean domestic fuel. LPG burns with a blue smokeless flame and leaves no ash behind. So, it does not cause any pollution. Therefore, LPG is a clean fuel.
3. It does not produce any poisonous gases on combustion.
4. LPG is easy to handle and convenient to store.
5. LPG is easy to handle and can be ignited almost instantaneously.

CNG is stored in pressurized vessels or spheres. They are gaseous in nature at STP. For it to be transported and used it is liquefied and kept in pressurized tanks. 

CNG is made by compressing natural gas which is mainly composed of methane, to less than 1 percent of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of 20–25 MPa, usually in cylindrical or spherical shapes.