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Diesel Conversions

Positive Vapour Injection system

We install Positive Vapour Injection systems on diesel powered vehicles. LP Gas is injected in conjunction with the diesel to improve combustion, which results in more power and fuel cost savings of up to 20%. Other advantages include reduced exhaust emissions, longer engine life and smoother running. In this system, the ignition of the diesel under compression provides the spark for the LPG which, having a higher flash point than diesel, speeds the burn of the diesel and provides more complete combustion.

Increased power and torque - every engine will achieve an increase in power and torque. The faster burning means an improved power stroke. This results in more power from the same amount of fuel or the same power from less fuel.

Fuel cost savings - savings are up to 20%. The actual savings vary due to many factors including engine size, load and driver. Therefore we only recommend the system where the vehicle will be used under heavy load and mostly highway driving as there is little if any fuel saving when the vehicle operates with light loads and around town driving.

Longer oil and engine life – more complete combustion of diesel reduces carbon deposits. Less carbon deposits means reduced oil contamination so oil life is extended. Also, because carbon is abrasive, less carbon means less wear.

Cleaner burning and reduced emissions – Carbon monoxide exhaust emissions are typically reduced by 20%.

Reduced maintenance – Oil and filter change intervals can be extended. Also there is dramatically less sludge in the engine.

Improved combustion characteristics – this results in a cooler engine, more torque, less driver fatigue, smoother running engine.

Pricing starts from $3,000 for 4WD’s and $10,000 for heavy trucks.


Diesel engines are used throughout the world wherever there is a need for extremely strong, powerful, hard working and reliable engines. They tend to be used in place of petrol engines in those situations where large horsepower is required to be delivered as economically as possible and so they are commonly found in applications such as; road transport and heavy haulage, construction and mining machinery, power generation and in rural applications both as stationary engines, for uses like irrigation pumps, as well as in farm machinery.  In comparison to many new generation petrol engines they are relatively simple and well regarded for their ability to provide reliable power output with a minimum of service problems for a very long period of time.

Perhaps the most frustrating problem with diesel engines is that as load increases and they approach the limits of their horsepower capability, which requires a larger flow of fuel, they become less efficient. This inefficiency is due in some part to the inability of the diesel fuel to burn quickly and consequently a significant portion of unburnt fuel is lost into the exhaust system. The combustion process can actually continue to some degree in the exhaust system and the most common evidence of incomplete combustion is the stream of black smoke seen escaping from the exhaust pipes of diesel engines under load. This smoke is composed mostly of partially burnt diesel fuel, which has formed soot. The other effect of incomplete combustion is the contamination of the engine's lubricating oil by the soot. Carbon is a very abrasive element and its presence in the lubrication system accelerates wear, significantly shortening the trouble free life of the engine.

Other aspects of the diesel engine are also coming under scrutiny, both in Australia and other parts of the world. Increases in the number of diesel engines in use has seen the demand for fuel approach very close to the potential for supply, which may lead to shortages in the near future. Fuel prices have traditionally been relatively lower than those of alternative products, but there is increasing upward pressure, particularly in those countries, which have kept prices low to encourage primary industries.

Many developed countries have quite strict exhaust emission standards for petrol engines and are now turning to diesel operators. An example of this is in the U.S.A., where the California Air Resources Board is currently introducing maximum emission levels for diesel powered engines, which will be phased in over the next ten years. These standards will apply not only to road transport operations, but all diesel operators, including farmers using tractors and irrigation pumps, power generators and construction machinery operators. Euro Standards are also being progressively applied to diesel engine emissions, again over the full range of applications.

Interest in the use of alternative fuels began with the petrol engine, with considerable research being centred on the conversion of these engines to either Natural Gas or LPG, the success of which is obvious by the number of cars operating on gas in Australia. In recent times the diesel engine problems identified above have led to an increased interest in powering them with alternative fuels also. Research and Development overseas has centred mainly on Natural Gas, with most engines being either purpose built, or converted to run entirely on gas. The problem with such conversions is the expense involved in supplying an ignition system for the gas, as well as the alteration of the compression ratio of the engine. Currently in Australia, the asking price for such a conversion is in the vicinity of $45,000. The use of Natural Gas as an alternative is also limited in this country to areas where supply is available via pipelines etc.

Bearing in mind the cost of full conversion to gas, as well as the limited availability of Natural Gas, the next alternative is the use of LPG as a partial substitute for diesel fuel. Conversion of engines to run on a mixture of fuels is relatively cheap and in this country there is sufficient infrastructure already in place in many rural areas to ensure reliable supply and delivery of the fuel.

The conversion of diesel engines to run on a gas substitution system addresses the major problems as outlined above. The introduction of LPG into the combustion process enhances and accelerates the diesel burn rate, giving more power due to a greater percentage of the fuel being ignited where it should be, that is, in the combustion chamber. With less fuel being partially burnt in the exhaust system, black smoke emissions are reduced, often to virtually nil. The ability of the gas to enhance the burn reduces other exhaust emissions, hopefully bringing levels close to the standards required by CARB, although further testing is required to quantify this. The reduction in the amount of soot produced will also reduce oil contamination, leading to longer engine life. Running costs are reduced due to the lower price of LPG compared to diesel fuel, although in many primary production situations the price differential is reduced because of the rebates available on diesel fuel excise duty.

The Viability of Torquegas LPG Substitution for Diesel Engines.

As outlined above, there are numerous driving forces that are placing pressure on diesel engine operators to consider alternative fuels. Whilst the global push for reduction in emissions has, to this point, not impacted significantly on rural operators in Australia, it is only a matter of time before this situation changes. Over the past few years diesel fuel prices have been trending upwards, which has impacted on all users. On the other hand, gas prices remain relatively cheap, leaving a variation in price between the two fuels which in remote areas may be as much as $0.70 per litre. Naturally a wider variation between the prices of the two fuels makes the viability of conversion more attractive due to a more rapid pay back time.

There are certainly other factors involved in the attractiveness of converting to a partial substitution system, including the emission aspects, as well as the significant reduction in wear and tear on the engine itself, due mainly to the reduction of carbon pollution of the lubricating oil.

Two additional points must be stressed. Firstly the system is a relatively uncomplicated and economical retro-fit for existing engines and engines converted under the existing system as developed to this stage can operate solely on diesel fuel without the need for any modification, should price changes, or gas supply problems be encountered. As we approach larger substitution rates, this may not necessarily be the case. The second point is that this system, while giving the expectation of longer engine life, is not and never will be a method of getting a few more years from an engine that is approaching the end of its service life.

Conversions can be fitted to engines of any horsepower. The price of the conversion is dependent upon engine size and complexity, rising from a base price of around $3000. This includes only the installation of the conversion system to the engine and not the supply of a storage vessel or pipework from it to the engine pick-up point. Larger engines, more complex systems and remote areas may require a higher charge.

Risks Associated with Torquegas LPG Substitution System

With the introduction of any new technology it is extremely important that no failures occur, even if the failure is traced back to factors beyond the influence of the technology itself. This is particularly the case in rural areas, where bad news often travels faster than the wind.

Through experience and with some systems that have been evaluated, two main risk areas are apparent, both of which have the potential to seriously jeopardise the success of any venture into installing this system. These are overfuelling and payback on investment.

Overfuelling — High Fuel Delivery

The greatest potential for engine failure comes from supplying excess quantities of LPG to the engine. Whilst LPG is a lower energy source than diesel fuel, the addition of the gas enhances the diesel burn, increasing the efficiency of the engine, which effectively raises the horsepower. Under constant load conditions this effect is not as great a problem as on variable load engines, where added strain to the engine itself, as well as that to the drive train, gearbox etc., can quite easily cause engine or component failure. The main objective is to supply a system that aids fuel and engine efficiency, but a system should never be seen as a cheap means of gaining horsepower. That task, in our view, remains solely within the scope of engine manufacturers. Even on constant load engines, overfuelling can be a cause of major engine failure (as well as wasting energy) and it is important that only trained personnel are involved with the setting of gas substitution levels. To avoid the potential risk, the following steps should be taken:

  1. Initially, engines are converted and the substitution level is set at around half to two thirds of the expected final substitution level, which is maintained for up to three months. This level is regulated by supply pressure and the fitting a tamper-proof regulator. The aim is to allow the upper end of the engine to clean up, by decoking valves, injectors etc., as well as allowing owners to be come familiar with the operating parameters of the converted engine.
  2. After the "proving period", engines are re-tuned and the higher substitution levels are set, the pressure regulator again being sealed to ensure that there is no potential for unauthorised personnel to tamper with the system.
  3. The engine management system can only be programmed by use of the hand held computer and any attempt to read or adjust the memory of the chips results in instant shut down of the system, thus ensuring that parameters cannot be altered by anybody except properly trained and authorised fitters.

Overfuelling — Gas Content

At this point, all engines have been running on retail quality propane - not Autogas, which often has a considerably higher level of butane and other gases present. A significant increase in the level of butane in the gas mixture (with its higher calorific value and lower flash point compared to propane), has a similar effect to over-fuelling as discussed above. Whilst this is not a major problem at relatively low substitution levels, as those levels increase, then so does the potential for over-fuelling the engine, with the possibility of engine failure becoming far greater. It is for this reason that it is extremely important that once an engine has been tuned for a high substitution level, the content of the gas should not change dramatically.

This problem needs to be monitored closely, as it may have a more significant effect in the road transport sector, where operators have little opportunity to correctly predict the exact mix of LPG they are fuelling up with at an Autogas site. There is no doubt that many failures in both dedicated and substituted LPG engines have been due to large quantities of butane being introduced to engines.

Payback on investment

  1. Regard must be paid to monitoring any upward trend in gas prices, particularly if in combination with downward trends in diesel fuel prices. This is especially important amongst larger users, who often have the buying power to maintain a relatively low diesel fuel price (and who are our primary target group in the power generation sector). Fast payback periods are the aim of most users and the potential to place payback periods in jeopardy must always be borne in mind. It may be necessary for gas suppliers to give serious consideration to adjusting margins within the first twelve to eighteen months to maintain the attractiveness of the conversion. Whilst perhaps not to the advantage of gas suppliers, the conversion system at present needs no modification to revert to diesel only operation, should price margins become negative.
  2. The Australian Government, through the Greenhouse Office, is currently offering incentives for users to convert to alternative fuels. Whilst this presently only applies to on-road diesel fuel users, there is considerable pressure being applied to have this extended to other areas. The potential for added cost savings due to fitting and fuel rebates, as well as the environmental benefits are enormous in power generation. This is particularly evident in the mining industry, where currently a rebate on diesel fuel excise can be claimed. Pure economics mean that there is no incentive to convert to substitution, despite the fact that one generator may produce emissions to the equivalent of ten trucks, given both their size and the number of hours running.


All individual components that make up a conversion system must be in relatively common use in the commercial or automotive gas industries. In all cases they must be approved under the relevant industry codes and standards.

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