Alternative fuels are
derived from sources other than petroleum. Most are produced domestically,
reducing our dependence on imported oil, and some are derived from renewable
sources. Often, they produce less pollution than gasoline or diesel.
Ethanol is produced domestically from corn and
other crops. It produces less greenhouse gas (GHG) emissions than gasoline or
diesel.
Electricity is produced domestically from a variety of sources such as coal, natural gas, nuclear power, and renewables. Powering vehicles with electricity causes no tailpipe emissions, but generating electricity can produce pollutants and greenhouse gases.
Biodiesel is diesel derived from vegetable oils and animal fats. It usually produces less air pollutants than petroleum-based diesel.
Natural gas is a fossil fuel that is plentiful in the U.S. It produces less air pollutants and GHGs than gasoline.
Propane, also called liquefied petroleum gas (LPG), is a domestically abundant fossil fuel. It produces less harmful air pollutants and GHGs than gasoline.
Hydrogen can be produced domestically from fossil fuels (such as coal), nuclear power, or renewable resources, such as hydropower. Fuel cell vehicles powered by pure hydrogen emit no harmful air pollutants.
Bi-fuel Engines
Most natural gas engines are either bi-fuel or dedicated. Bi-fuel
engines are Otto cycle (spark ignited) that run on either natural gas or
gasoline. The bi-fuel natural gas engine maintains two fuelling systems on
board a vehicle: a natural gas system as well as a petrol system. While not
necessarily optimised for natural gas operation, they tend to be more
‘environmentally friendly’ than petrol engines and have the advantage of
running on petrol in the event that a natural gas fuelling station is not
readily available.
Dual Fuel Engines
Dual fuel natural gas engines are based upon diesel technology. The
primary fuel is natural gas but they are designed to operate interchangeably
with diesel as a ‘pilot’ ignition source (functioning on heat of compression
and not with a spark plug). These engines also can operate on 100% diesel fuel.
When idling these engines tend to operate on 100% diesel. As the vehicle begins
to move to full load performance, an increasing amount of natural gas replaces
the diesel fuel to 80% or more. This makes them especially valuable in
circumstances where the use of natural gas is desired for environmental or
economic reasons but where the natural gas supply is not available in all
locations. It also is relatively easy to convert a diesel engine to dual fuel
operation.
Types of gaseous fuel used
in Dual fuel engine :
·
Natural Gas
·
Sewage Gas
·
LPG
· Town Gas
· Hydrogen Gas
Multi-Fuel Engines
Multifuel refers to any device capable of burning more than one type of fuel. This may include an engine or motor used to power equipment, or a furnace or stove used for heating. While multifuel systems originated in the military to help troops function with limited fuel supplies, they are now used all over the world in a wide variety of settings. These engines are designed to consume the best quality fuel, or highest octane made available to them. Many automatically modify operation based on the type of fuel used. Others feature a manual switch that users can adjust based on the type of fuel they plan to use. Multifuel engines are commonly used in military vehicles or aircraft. They are also used in flex-style automobiles, which may rely on ethanol or standard gasoline for power. The primary advantages to a multifuel system is the flexibility it offers to users. If homeowners or companies run out of a standard fuel, they can rely on other fuel sources to avoid a loss of heat or power. Multifuel engines also help to reduce dependence on traditional fossil fuels, which can help preserve limited world supplies.
Difference between Bi-fuel and Dual Fuel Engine.
|
Bi-Fuel |
Dual-Fuel |
|
Bi-fuel systems use two different types of fuel that
do not mix together during operation. These systems can switch fuel sources
either automatically based on set parameters or via operator control. |
Dual-fuel systems combine two different types of fuel within the mixture that runs through the engine. This is usually done by allowing the primary fuel to fill the system before a governor gradually introduces the second fuel source. |
Stratified Charge Engine with lean burn
The principle of the stratified charge engine is to deliver a mixture
that is sufficiently rich for combustion in the immediate vicinity of the spark
plug and in the remainder of the cylinder, a very lean mixture that is so low
in fuel that it could not be used in a traditional engine. On an engine with
stratified charge, the delivered power is no longer controlled by the quantity
of admitted air, but by the quantity of petrol injected(pilot injector), as
with a diesel engine.
Variable Compression Ration Engine
Conventional gasoline engines operate at a fixed compression ratio,
which is set low enough to prevent premature ignition of the fuel, or “knock,”
at high power levels under fast acceleration, high speeds, or heavy loads. Most
of the time, however, gasoline engines operate at relatively low power levels
under slow acceleration, lower speed, or light loads. If the compression ratio
were increased at low-power operation, gasoline engines could achieve higher
fuel efficiency.
A variable compression ratio (VCR) engine is able to operate at
different compression ratios, depending on the particular vehicle performance
needs. The VCR engine is optimized for the full range of driving conditions,
such as acceleration, speed, and load. At low power levels, the VCR engine
operates at high compression to capture fuel efficiency benefits, while at high
power levels, it operates at low compression levels to prevent knock.
To further improve fuel economy, the VCR engine is small, with about
onethird the displacement volume of a conventional gasoline engine. A
supercharger boosts engine peak power when needed for occasional hard
acceleration or hill climbing.
