Did you know that LPG-powered vehicles have a longer
history than petrol and diesel powered vehicles?
The first LPG-driven car was built in 1862 by Etienne
Lenoir. It provided the technological archetype for the
later development of diesel and petrol vehicles. The idea
of propelling a vehicle with LPG remained alive, and some
work was done on the concept, but the automotive
industry focused on diesel and petrol – until recently.
Useful LPG facts:
Liquefied Petroleum Gas (LPG) is the generic name for
the mixture of propane and butane gases.
LPG is a by-product of crude oil refineries.
Chemical description: octane number 115, stored in
liquid form at a pressure of around 8bar.
Colourless, odourless and heavier than air, LPG is
gaseous at normal pressures and temperatures. LPG
liquefies at low pressure and does not turn into a gas
until it is in the engine in automotive application.
Energy density in comparison to petrol: 1 litre LPG
equals about 0.85 litres petrol.
Today, LPG is the most commonly used alternative fuel
for cars .
The number of LPG powered vehicles in Australia at
the end of 2008 was 197,458* and rising with over
3,200 LPG fuel outlets nationally.
LPG costs significantly less than petrol. For example;
in February 2009, LPG was 61.9 cents per litre, much
cheaper than petrol (116.4 cents per litre) and diesel
(122.5 cents per litre) in Australia. Although LPG
generally increases fuel consumption by up to 30%,
the savings with LPG conversions can solely be based
on the huge price difference. Vehicles with high annual
distance such as taxis and fleet vehicles definitely
benefit but personal use vehicles can also see
dramatic reductions in costs.
Since 2006 the Australian Government has been
offering grants for LPG vehicles both new and used,
to support the use of LPG in vehicles.
For further information please visit:
http://www.ausindustry.gov.au/EnergyandFuels LPG burns clean. It produces no soot and very few
sulphur emissions, posing no ground or water
pollution hazards. It also helps vehicles reduce
greenhouse emissions by 15% more than their petrolpowered
equivalent.
Refuelling LPG is a fully sealed process compared to
petrol refuelling which releases chemical vapours into
the atmosphere.
The high-octane numbers of LPG allow better use of
the “knock” limit (the degree of spark advance before
detonation), resulting in more dynamic performance.
As an energy source LPG clearly differs from natural
gas and electricity. It can be easily stored and
transported in purpose-built pressurised containers.
These tanks cannot explode and are less of a fire
hazard than petrol tanks.
When lightly compressed, LPG becomes a liquid and
therein lies the benefit - one litre of liquid LPG is the
equivalent of 270 litres of gas.
You must be licensed and registered to conduct LPG
conversions and servicing in Australia. For further
information please visit
http://www.ausindustry.gov.au/EnergyandFuels There are mainly two types of LPG vehicles
1. Dual-fuel vehicles have two fuel tanks allowing the
driver to switch between LPG and petrol power with a
dash board switch. As a rule these cars have higher
mileage (range) than single-fuel cars, and performance
differences are barely noticeable.
2. Single-fuel vehicles are LPG-only, but could have a
small emergency tank that holds a small quantity of
petrol. Being purpose-designed for LPG, the engines
are more efficient than dual-fuel engines
Spark Plugs in LPG Versus Petrol Engines
Dual-fuel or single-fuel, petrol or LPG; all spark-ignition
engines work in the same basic way. This fact allows
almost any petrol engine to be easily and economically
converted to LPG.
However, there are some significant differences in how
an engine functions when it runs on LPG compared to
petrol.
Combustion chamber temperature
When petrol enters the combustion chamber,
evaporative cooling occurs. This cools the spark plug
and other components (“charge cooling”). Since LPG
is not a liquid, it burns dry, so there is no charge
cooling effect. That means the combustion chamber
and spark plug electrode are hotter.
Higher voltage requirements
As the internal combustion temperatures and
pressures are higher in LPG engines, they need higher
spark voltage for ionisation (the spark to jump the
electrode gap) than petrol engines. Where a petrol
engine might need 14 kV, the same engine but with
LPG would need 16 kV (see figure 1).
Heat range
LPG vehicles require spark plugs with a colder heat
range, to prevent pre-ignition.
Life
Higher temperatures in the combustion chamber and
high voltage result in accelerating spark plug wear.
Therefore LPG spark plugs need to be changed more
often than spark plugs in petrol vehicles.
LPG Versus Petrol Spark Plugs | A7
2009
LPG servicing becomes simpler as you can have the right
plug with the right gap – saving you time and money on
every service.
The Right Leads Make a Big Difference
The ignition system is the key to full engine power.
When petrol powered vehicles are converted to LPG the
ignition system performance must be more efficient. To
ensure this, LPG specialists need to look for potential
trouble spots. Ignition leads are sometimes over looked
and can make a significant difference to performance.
Always check the following during a LPG service:
1. To ensure proper functioning of the ignition system,
ignition leads must be in good condition (not worn out or
damaged) and all connections must be tight.
2. The ignition system can be tested with an engine tester
or oscilloscope. The measured ignition voltage should
match the target voltage given by the vehicle
manufacturer. If anything is out of the ordinary then
replace the corresponding ignition cable or component.
Please note: Especially with older resistance ignition
wires, the cable core can break. In such scenarios the
entire ignition cable set should be replaced. Bosch offers
ignition cables for all applications.
A poor performing ignition system can result in:
Rough running
Misfiring
Significant drop in performance
Increased fuel consumption
Danger of damage to other components
Refer to the Bosch Ignition Leads catalogue for further
details.
Q - What is pre-ignition?
A - Pre-ignition is an uncontrolled ignition process in
which the temperatures in the combustion chamber can
rise to such an extent as to cause serious damage to the
engine and the spark plug. Full-throttle operation can
generate localised hot spots and cause pre-ignition at the
following locations:
At the tip of the spark plug’s insulator nose
On the exhaust valve
On the protruding sections of the head gasket
On loose deposits (ash and carbon residue)
Pre-ignition of the air/fuel mixture can cause severe
damage to an engine and this is one reason why the heat
range of a spark plug is so important.
Q- What is a heat range?
A - The spark plug’s heat range is an index of its capacity
to dissipate thermal energy. The different characteristics
of automotive engines regarding operating load,
compression, engine speed, cooling, and fuel make it
impossible to run all engines with a standard spark plug.
The same spark plug may get very hot in one engine type,
but may reach only a relatively low temperature in
another. In the first case, the air-fuel mixture would ignite
on the glowing parts of the spark plug projecting into the
combustion chamber (pre-ignition) and, in the second
case, the insulator tip would soon become so badly
fouled by combustion deposits that misfiring would occur.
To ensure that the plug runs between the desired
temperatures, plugs with different heat capacities were
developed.
The so called “heat range”, which is assigned to each
spark plug, is used to characterise these heat dissipation
capacities. A plug with a low heat range number (e.g. 2-4)
indicates a cold plug that quickly dissipates heat to the
engine block and cooling system, while a high code (e.g.
7-10) indicates a hot plug that retains heat.
By properly selecting the heat range of the plug, it
ensures that the plug will operate between the plug’s
designed operating ranges of 500-900 degrees Celsius. In
this range, the spark plug will be self-cleaning, yet will not
be hot enough to pre-ignite the air/fuel mixture.
Q - What is detonation?
A - Detonation or “knocking” is uncontrolled combustion
with a very steep rise in pressure. It is caused by
spontaneous ignition of the fuel mixture, which has not
yet been reached by the ignition spark. As the high
pressure waves hit the walls of the combustion chamber,
their impact produces a metallic knocking sound. Failure
to recognise and deal with knocking will inevitably lead to
serious engine damage.
