Health & Safety aspect for Hydrogen Injection into a Diesel Engine
Safety Aspects of Hydrogen Use
According to Hydrogen safety data sheets from Air Liquide and BOC the main hazard
associated with hydrogen is its high flammability. Hydrogen becomes flammable
when its concentration is between 4-75% by volume in air. It can also cause
asphyxiation when in high concentrations.
Examination on the concentration of Hydrogen within the Laboratory
Appendix 1 shows the calculations used to determine the maximum concentration of
hydrogen that could be achieved in the thermodynamics lab if an entire 'K' sized
bottle were released slowly into it. This was found to be 0.38% by volume which is
well below the 4% minimum required for combustion. However, due to the low
density of hydrogen local higher concentrations could occur in the roof space and this
area would need to be vented if a leak occurred.
Flow rates required and measurement
The hydrogen gas is to be added to the inlet airflow of the engine. The flow rates to
be used are based on the hydrogen supplying 10% of the total power of the engine.
The engine is being tested under conditions of light loading, meaning that a small
amount of Diesel is being added, consequently the quantity of hydrogen injected
would also be small. The expected concentration of the hydrogen in the inlet air
stream has been calculated (appendix 2).
The conclusion was that the concentration at the highest power setting is 1.03% by
volume is therefore below the lower limit of flammability concentration (4% by volume
in air) as stated by both of the safety data sheets of BOC and Air Liquide. limit of
flammability. This concentration is typical of the concentrations of the various other
test conditions.
The flow rate is to be measured using a rotameter with a safety screen fitting in order
to contain any glass in the event of excess pressure causing failure of the inner glass
tube. The manometer and thermocouple in the pipe work are present to make
pressure and temperature corrections to the flow rate measurement.
Securing of the Cylinders
Precautions should be taken to ensure that both the hydrogen and nitrogen bottles
can not fall over. The use of a bottle trolley or strapping to a fixed bench is required.
Pipe work construction
The pipe system can only be constructed, modified, attached to or disconnected from
the gas bottle and its fittings by an authorised fitter within the Department.
The pipe work is to be constructed using both 6mm and 12mm outside diameter
tubing which have internal diameters of 4mm and 8.5mm respectively. The majority
of the pipe work including the pipes from the two gas cylinders and the pipe to the
injection point will be of 6mm outside diameter pipe. This will reduced the quantity
gas within the pipe work. A small section of the system uses 12mm outside diameter
pipe, this is in order to facilitate connection of the needle valve.
Pipe work flushing
Flushing the pipework with nitrogen or argon is necessary before adding hydrogen at
the start of a test and at the end of every test in order to prevent air and hydrogen
mixing in the pipework. The nitrogen or argon bottle may be connected via a 3 way
tap.
Earth Bonding
To minimise sources of ignition earth bonding will be applied between the various
parts of the system that may come into contact with each other and to earth. This
includes; the engine, the cylinder bottle and the operator. The engine block is to be
earthed via an available tapping. This will then be connected to the earth of the
electrical mains supply. The gas cylinders are to be earthed using worm drive
clamps fitted to the circumference of each cylinder with an earth wire between the
cylinders and the engine block. The operator of the system will wear anti-static
gloves to reduced the risk of static discharge.
Other forms of Ignition
All other forms of ignition should be avoided. The department of engineering is a no
smoking area.
Ventilation
Both during the testing and afterwards, adequate ventilation will be provided in case
of a possible leak.
Users guide
A users guide for the operation of the apparatus has been compiled. This will be
attached to the apparatus. A copy of which is included within this proposal.
Operation of engine
When the engine is running with hydrogen being injected, the engine is not to be left
unattended.
Appendix 1
Maximum Concentration of Hydrogen In The Laboratory
Quantity of hydrogen in a hydrogen cylinder
Product data sheets that state the sizes of cylinder that can be supplied were
consulted. The bottle size K is to be used. These data sheets state that this cylinder
contains a volume of hydrogen gas of 7.2m3 at atmospheric conditions.
Volume of the Thermodynamics Laboratory
The volume of the thermodynamics laboratory has been calculated as follows.
The total volume of the laboratory = l x b x h = 29m x 12.7m x 4.7m = 17303
The concentration of the hydrogen gas using the total volume of the laboratory;
=7.2m / 1730m =0.42% by volume
The length of the laboratory excludes the test cells and control room.
0.38% by volume
Appendix 2
Concentration Of Hydrogen In The Engine's Inlet Air Stream
At the highest power setting to be tested power supplied to the engine in terms of
Diesel fuel = 15405 W
To find the amount of hydrogen to be supplied
15405 W x 1/9 = 1711 W
The lower calorific value (LCV) of hydrogen is 10.22 MJm-3 at 15oC 1.01325 bar
Using the calorific value above, the flow rate for the hydrogen can be calculated to
be;
1711 W / 10.22 MJm-3 = 1.67x10-4 m3s-1
The air flow rate at this engine setting is 0.0162 m3s-1
The hydrogen concentration at this particular power setting can be calculated to be;
1.67x10-4 m3s-1 / 0.0162 m3s-1 = 1.03%