Producer gas in power generation
Practical Action
CI engines also require several other major modifications. These include lower compression
ratios, provision of extra cooling to injectors, and the fitting of gas carburettor.
Generally spark ignition engines are less robust than compression ignition engines but don’t
need supplementary fuel. Therefore it is common to convert compression ignition engines to
spark ignition as a compromise between robust and reliable operation and to alleviate the
need for supplementary fuels.
Loss of engine performance
When using producer gas, power loss may occur in four ways:
1 The presence of nitrogen from the atmosphere as an inert dilutant of the gas-air
mixture will cause a reduction in power of about 35 to 50%.
2 The power required to carry the additional load of the gas unit, of between about
200-700 kg for units to operate engines up to 3-litre capacity.
3 The normal derating or unblown engines due to increasing altitude and ambient
temperatures round in many low income countries.
4 Due to the above, a modern engine designed for use with high grade fuels, may no
longer be able to operate on the centre of its power curve, resulting in loss of
performance.
Maintenance
A producer gas unit must be refuelled before the fuel level has dropped more than about
three quarters, or to keep at least 300 mm of fuel above the fire zone, or the production of
gas will be interfered with and the possibility of explosions increases.
Maintenance will include refuelling, the removal of ash and any clinker from the generator,
and the removal of dust and condensates from the cleaning and cooling sections. Normal
lubrication should be unaffected. Engine wear may be reduced with an efficient gas unit due
to there being less corrosives, a lower exhaust gas temperature, less carbon deposited, and
less bearing wear due to a smoother slower rate of burning. It is important that no leaks are
left unrepaired, so regular frequent inspections are essential in order to maintain the unit in
an efficient and safe condition. This may not be done unless arranged through a central
garage service.
Fuel
Any carbonaceous material can be converted to producer gas but automotive use requires a
reliable source of high quality gas, low in dust, moisture, tar and sulphur. The fuel must be
evenly graded, of moderate particle size, with a high reaction response, high calorific value,
and having low ash and clinker characteristics. The fuel should be cheap, readily available
and uncontaminated by soil and water.
Good quality wood-chip ranging from 20mm to 75mm with moisture content of up to 20% is
best suited for gasification. Fine grained material such as sawdust would be as good if
briquetted, but this process is difficult and expensive in practice, especially as the end
product must be low in tar, moisture and clinker, a situation aggravated by most binders.
Good quality hardwood charcoal also makes an idea fuel for gasification. Good charcoal has a
low tar content compared to many other biomass materials which may be advantageous as tar
can be difficult and expensive to remove from producer gas. The best charcoal, evenly burnt
and free of contamination, is produced in a retort. Charcoal from a pit may contain soil and
unburned pieces high in tar.
To change seasonally from one kind of fuel to another could involve major modifications to
equipment if this involves a change in fuel characteristics.
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