In a normal 4-stroke diesel engine, air is introduced into the
combustion space inside the cylinder in the air intake stroke of the piston.
After that there is the compression stroke which brings the air to a high
temperature.
Diesel oil is then injected into the combustion space as a very fine mist. It
does this by using fuel pumps and injectors.
The mixture of air and diesel explodes and pressure
builds up at the piston top. This pushes down the piston and has the momentum to
drive the engine for the
next 2 cycles.
The next cycle is the exhaust stroke. In this stroke, all the products of
combustion is driven off from the piston top.
Bi-Fuel Engine Operation
In a bi-fuel engine, instead of just fresh air intake in the air intake stroke,
a mixture of natural gas and air is delivered to the
cylinders and is then ignited by a
diesel “pilot” which acts as an ignition source for the air-gas mixture.
However, not all combustible gas is usable. Methane is usable while LPG or
propane and butane are not usable.
The gas concentration in the intake air is typically less than 3.0% by volume,
which is substantially below the 5.0% Lower Explosive Limit (LEL) of methane. Due to the lean condition
of the air-gas charge, the possibility of ignition in the engine air-intake
system due to backfire or other causes is minimized. (compared to 2% LEL for
LPG)
Another factor is the high ignition temperature of methane at 650~750 deg C
compared to 450~500 deg for LPG.
By just including some methane into the normal air intake, the engine can thus
be run on two types of fuel, namely, methane gas and diesel oil.
Therefore conversion requires no modifications of the engine and allows the engine
to operate on
gas mixtures ranging from 50% to over 70% of total fuel consumed. After
conversion, the engine can still be operated on 100% diesel fuel without loss of
power or efficiency.
Despite the simple concept, there are various important key control technologies
and controls that must be in place to make the system work. Amongst the critical
controls are:
- Gas supply pressure
- Regulator output pressure (switch)
- Air filter vacuum
- Manifold air pressure
- Manifold air temperature
- Exhaust gas temperature
- Engine vibration
Gaseous Fuel operation will typically
reduce production of nitrogen oxides,
sulfur oxides, reactive hydrocarbons, carbon dioxide and particulates.
Exhaust opacity levels (visual emissions) are also typically reduced.
View products for more information.