Options of various alternative fuels for motor vehicles:
We discuss below various other fuels that can be used as alternative to fossil fuel for motor vehicles; some of the fuels discussed are renewable:
(a) Bio-diesel: Motor vehicles can be very efficiently run by bio-diesel. Internal combustion engines are common in motor vehicles and are traditionally fuelled by diesel derived from fossil fuels. Thankfully diesel is a compound which can be replaced with bio-diesel which is an organically based product and is renewable. It is relatively easily produced from plant and animal oils, fats and greases. Environmentally, bio-diesel run vehicles also gives benefits in reduction of pollution.
(b) Liquefied Petroleum Gas (LPG): LPG is an alternative to petrol (gasoline), it offers lower local pollution levels than normal fuels. This fuel is compatible with petrol and many vehicles can run on either (dual-fuel vehicles); so the limited distribution of LPG is not a problem. Its main claims to fame are its reduced local pollution and it is also cheaper to run. Unfortunately, it is not renewable as it is petroleum based product and does not qualify for tackling climate change.
(c) Liquefied Natural Gas (LNG) and Compressed Natural Gas (CNG): In practice, LNG and CNG are replacements for petrol / diesel and suitable for heavier freight vehicles. Natural gas is intrinsically cleaner than petrol / diesel, but since it is a fossil fuel it is not renewable. It also contributes to global warming. At a local level it produces much less pollution than petrol or diesel and its use attracts financial incentives. The fuel tanks are specially designed for intense refrigeration (LNG) or high pressure (CNG) which makes them larger and heavier.
(d) Ethanol and Methanol: Can be used as alternatives or complements to petrol (gasoline) and can give less local pollution. If the raw source is petroleum then they are not renewable. Fortunately, they can be produced organically; e.g. from sugar cane etc., and then they can contribute in reducing climate change. Producing these alcohols organically can also bring economic benefits to rural developments by way of benefiting farmers.
(e) Hydrogen Fuel Cells: Fuel cells are not, strictly speaking, renewable or alternative energy, they are engines which convert energy; the energy source is actually hydrogen. Potentially this system can give clean and efficient energy. This technology is complex and research and development is needed to make them more feasible. The hydrogen fuel can be derived from a variety of sources. The hydrogen fuel cell is an electrochemical energy conversion device. Hydrogen and oxygen are fed into opposite sides of a cell, which are separated by a membrane permeable to hydrogen ions but not electrons. Hydrogen gas molecules entering the anode side of the cell are ionized in the presence of a catalyst to form protons and electrons. The protons pass through the membrane to combine with the oxygen and electrons to produce water at the cathode. The electrons flow through an external circuit from the anode to the cathode, creating an electrical current, which powers an electric load such as a motor. If the source of energy is renewable then we have a desirable situation but if it is petroleum derived, for example, and then it is not a renewable system. There are developments which indicate that fuel cells may provide an important source of energy in transport applications.
(f) Hybrid engine systems: This system uses internal combustion engines in tandem with battery-driven electric motors, to conserve energy. A few cars are now in production with this system. The batteries are charged from the kinetic energy of the vehicle (e.g., when braking). Manufacturers use Nickel-metal Hydride batteries (designed, it is claimed, to last as long as the car) and these are charged by the petrol power unit (via an alternator) during normal driving. Power is delivered to the wheels by either unit or both depending on the demands such as acceleration, during cruising or braking. Currently the vehicles are dearer, and this system only mitigates the problem of carbon emissions. It does not solve the emission problem. Nevertheless, the energy that is regenerated is truly green. One advantage of the electric system over the petrol engine is the torque available over a wide speed range; a normal car has several gears to narrow the speed range in use.