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Diesel Gas System

Diesel Gas

Over the years the term Diesel / gas conversion has carried invoked a lot of conjecture and this sometimes results in inaccurate information being provided to the consumer.

In 1897 the inventor of the diesel engine, Rudolph Diesel, recognized the inherent problem with the patented diesel compression ignition engine. The issue was that the engine itself could not provide complete combustion of the diesel fuel. Requiring very high compression to “heat” the air charge, the injected fuel does not have time to evenly “populate’ the combustion chamber to provide full combustion and only around 70% of the fuel charge is burnt.

Rudolph Diesel stated that,

The “Diesel Engine would benefit greatly from a gaseous fumigation system”.

One hundred and fifteen years later the fact and principle remains the same, but method of GAS / LPG delivery has had to become more refined and controlled to:

1/optimize performance
2/ meet emissions
3/and most importantly provide ENGINE PROTECTION.

How does it work?

If we were to imagine the lighting of an OXY- Acetylene welding/cutting torch.

When an OXY- ACETYLENE torch is lit only acetylene is being used, acetylene is the fuel. The burning acetylene produces a cool, orange, fluffy, sooty, flame laden with un-burnt carbon. Ie energy.
By adding a small amount of oxygen (combustion enhancer) the flame is now a hot, crisp, clean, blue flame. The “ENERGY” stored in the acetylene has now been burnt completely.

What happens in practice?

As previously mentioned a diesel engine generally only burns around 70% of the diesel supplied to the engine. The other 30% of unburnt fuel exits via the exhaust into the atmosphere and is wasted.

The addition of a small amount of LPG “mixed” with the diesel fuel charge enhances the combustion process so that we can now burn up to 95% of the diesel charge.


The Benefits of Diesel / LPG are clear and provide:

Improved power delivery

Injecting gas from idle improves power delivery right off the mark. There is no delay of waiting for revs or turbo boost pressure to build up – gas flow is ramped up instantly as you take off compared to the diesel only fuel system. Typically a 20-25% power gain is achieved with up to a 30% increase not uncommon with this system.

Improved diesel economy with diesel gas injection

DieselGas allows LPG to be used at idle, substituting a percentage of diesel required for idle. Over extended idle periods, such as in traffic, this substitution adds up to a significant reduction in diesel consumption. This reduction is on top of the usual economy benefits of DieselGas.

A diesel gas injection system offers increased LPG range

The absolute accuracy of the DieselGas Sequential systems guarantee LPG is only used when it is needed. Gas flow is shut off instantly and completely for gear changes, under brakes and when coasting downhill. With this level of control, LPG consumption is reduced by around 20% and in some cases more.


Four methods of Diesel Gas Fuel Delivery and Control

1/ Fixed hard settings and jetting - unable to react and respond to RPM, load and boost changes.
2 / Venturi and stepper motor - 10-18 second reaction time. A terrible amount of damage can be done in this time.
3 / Centre point Vapour injection - 1/10 of a second reaction time.
4 / Multi point Vapour injection -Absolute time.

NOTE: Smithy’s LPG and Automotive services do not use or recommend method’s 1 & 2 for automotive use.

(Methods 3/ and 4/ are suited to both naturally aspirated and turbocharged applications.)

Method / 3

Centre point Diesel/LPG vapour injection systems:

With this method of fuel delivery a small amount of LPG vapour is injected just before the turbo charger, it is necessary to add the fuel at this point to ensure complete blending of air and fuel for even distribution to all cylinders.

It is suggested that this is inappropriate and that it may lead to backing and resulting in damage to the turbo charger and inter-cooler, THIS IS INCORRECT. The value of the added fuel or air fuel ratio is well below the LEL ( low explosive limit ) ie. not enough fuel to burn.

The LPG is vaporised in an AGA approved automotive LPG converter, this LPG vapour is the injected via a high speed low impedance AGA approved automotive LPG injector.

The injection control is provided by a control unit that takes references off temperature, TPS, tacho MAP and EGT sensors.

Engine protection is provided via the new exhaust gas temperature sensor, this will isolate the LPG system and revert back to standard diesel operation in the event of high EGT or a system malfunction.

Method / 4

Common Rail Multi-point Diesel/LPG vapour injection systems:

As engine management techniques have advanced we are now able to fully integrate the aftermarket Diesel / LPG system with the Factory diesel fuel systems. For example diesel injection used to be primitive and mechanical. But now the common rail diesel is sophisticated and electronic; we can use this to our advantage.

The parallel of this may be compare to a carburetted six cylinder Falcon verses a multi point injected six cylinder Falcon. In this case a 15% gain in performance and economy was achieved.

The advantages are all based on “fuel control”.


Common Rail Multi-point Diesel/LPG vapour injection system features:

  • Sequentially injected LPG
  • Injection takes place directly into the intake manifold at the back of the intake valve
  • No LPG vapour in turbo or intercooler.
  • Removal of up to 40% of diesel volume with
  • Sequential LPG mixture correction & substitution
  • Integrated fuel gauge & function controller(displays LPG level & selection )
  • Built-in Common Rail fuel pressure emulator.
  • Automatic collection of knock values maps on Diesel only and on Diesel with Gas.
  • Automatic correction of gas injection opening times depending on TPS, RPM, MAP, KN and EGT.
  • Dedicated injection maps for driving on cruise-control or on speed limiter.
  • CAN BUS line connected with vehicle’s OBD.
  • System can control up to 8 gas injectors at the same time independently.
  • Full support of V type engines (independent corrections for each bank).
  • Full engine protection from excessive RPM, EGT and Engine knock
  • In built monitoring and Data Logging ability.
  • System can control up to 8 gas injectors at the same time independently.
  • Full support of V type engines (independent corrections for each bank).
  • Full engine protection from excessive RPM, EGT and Engine knock
  • In built monitoring and Data Logging ability.
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