300k kilometers travelled on autogas... and we keep on going!


An autogas system based on high-quality components will not have a negative effect on the engine and even makes it possible to travel 300k km and more.

The AC Company – the largest Polish manufacturer of autogas components under the brand name of STAG – operates its own company fleet. It is easy to work out that these cars are fuelled with autogas, and are a kind of test unit in the field. The company bought Kia cars 4 years ago and converted them to use gas fuel. Three of them already show quite high mileage – between 230 and 290k km. However, the owner has no intention of replacing them. The cars show no major problems and will can be driven even longer despite (or to put it in our words: thanks to) the LPG fueling. How is that possible?

In the sequential autogas system, typical wear and tear components include injectors and reducers. Obviously, other elements – tank, wiring or controller – may fail, but they usually last for the entire life of the vehicle. They are not susceptible to poor gas quality or wear resulting from multiple engine starts. Therefore, the injectors and reducers (besides the fuel filters) are the only components of the system in which wear and subsequent replacement is bound to occur sooner or later. "When" is the question of the working conditions and the quality of such parts.

It is good to know that in cars with engines that are always warm and cover long distances on a daily basis (e.g. fleet cars), the reducers and injectors wear out very slowly and it is possible to reach impressive mileage levels without replacing them. The wear and tear of the reducer only depends on mileage to a certain extent – it largely depends on the number of warming and cooling cycles, which are responsible for the variation in the properties of reducer membranes. Similarly, the injectors, which are slightly more sensitive to mileage and less so to the number of starts, also wear out slowly when covering long distances. AC provides a 2-year or 5-year warranty for STAG products (depending on the type of controller) without a mileage limit – this means that the annual mileage can reach 100k km and the chances of needing to make use of the warranty are not high: it is rather highly probable that even the "wearing" parts will survive. It is worth taking note of the fact that if a small mileage of up to 5k km per year is covered on short distances only, the reducer may (but doesn't have to) fail even if the mileage is nowhere near as high as that which fleet cars cover. Time, downtime and also a large number of cold engine starts can be harmful to the LPG system – likewise in factory-mounted fueling systems.

The AC cars which have been mentioned now have over 200k km on the clock and have had their injector rails and reducers replaced. The previous ones (AC R01 reducers and AC W01 injector rails) lasted approx. 200k km! Only after covering such a distance was it discovered that their operating parameters no longer conformed to the specifications and that they should be replaced with new units.

However, many owners wonder about the following: the LPG system is durable, but what about the engine? There can be only one answer: if the system components are selected correctly (good electronic components and actuating devices – reducer and injectors with sufficient performance for the engine requirements), the operation of the autogas system does not significantly affect the wear and tear on the engine! Engine failures occurring after conversion to gas mainly result from the use of autogas components with inadequate quality or poor performance parameters. Proof? Every day, in countries where gas-fueling is popular and odometer rollback is more difficult due to the general availability of vehicle information which has been entered during regular technical checks, we can find hundreds of sales offers for LPG-powered cars with 400-500k km on the clock. Their owners use gas fueling, because it's cheaper and the car is sold not because of engine damage but due to general wear, and, additionally… they would like to have something better.

It is similar in Poland: cars fitted with high-quality LPG components cover high mileage and perform superbly in fleets. Another thing is that Polish dealers of used cars rarely declare mileage exceeding 200k km. 01.07.2015

Additional savings on LPG

Some owners are discouraged from autogas fueling by the increased petrol consumption and reduced comfort of using the LPG system. However, it turns out that additional LPG-assist equipment can significantly improve its operation - also in winter. A car converted to LPG still uses some petrol for the engine start. The car is started on petrol and when the antifreeze liquid in the cooling system heats up enough to be able to flow through the LPG reducer at the operating temperature, petrol fueling mode is automatically switched to gas.

It is a natural feature of any autogas system resulting from the fact that the expanding gas undergoes significant chilling. This phenomenon occurs in the reducer of a car which has been fitted with an LPG system - i.e. the component converting the liquid phase of gas into vapor to feed it into the engine. The reducer is warmed with the antifreeze liquid to be able to handle the expansion of a dose of gas fuel. The effective operation of the reducer, particularly at low temperatures, is therefore possible only after the engine has been warmed.  Depending on the model of the car and the ambient temperature, this occurs shortly after the engine start or takes place after 2-3 kilometers of driving.

In winter, savings resulting from the use of economic fuel depend strictly on the driving conditions. If the weather is extremely frosty, the driver does not specially notice the fact that the switching of fuel takes place after 2-3 km. However, if the travelled distances are only several kilometers or less, the car uses petrol for most of the driving. This is not what we wanted!

In order to improve the comfort of using gas-powered cars in winter, a STAG R01 CS microprocessor-controlled reducer preheater has been designed. This device checks the temperature of the reducer on the ignition switch and activates electric heating if required. Thanks to this, even at -5OC it is possible to start the engine on gas, which perfectly ensures that running the car is more economic. If the ambient temperature is lower and starting the engine on gas is not possible, the STAG R01 CS heater still helps: it reduces the time required to switch from petrol to gas by as much as 40%!

The STAG R01 CS reducer is ready to operate at any time when the engine is running to ensure even better reducer performance, not only during the engine start but also during normal driving. In the case of a high momentary demand for fuel, e.g. during dynamic acceleration, the temperature inside the reducer may drop – its task is to maintain the optimum temperature of the reducer, i.e. ensure full performance of the engine. Since the heater requires up to 60A of current, the question arises: how does it affect the battery? It turns out there is no need to worry. The unit is controlled electronically and this maximum current consumption is only allowed when the engine is operating. Additionally, the controller continuously monitors the status of the system and adjusts the heater operation to the current requirements and capabilities of the electrical system.

How much can you save in practice? In a 1.4 l engine operated in a combined cycle, petrol consumption in winter is reduced from approx. 10 to approx. 5 liters of petrol per 1000 km. In cars with larger engine units, particularly those used mainly in cities, savings can be much higher. We can also enjoy some savings in summer, though not so high. However, STAG R01 CS preheater has been designed primarily to improve the comfort of LPG system use and maximize the use of LPG performance fully.

It is worth knowing that the preheater is not the only component that can assist the operation of autogas systems. Another interesting example is a timing advance processor (TAP), which dynamically changes the advance timing angle in the engine depending on current needs. Why is it needed? One of the differences between petrol and gas fuel is the octane number – it is slightly higher in autogas, which makes it possible to advance the spark by a specific value without the risk of knocking combustion. Additionally, gas fuel is burnt slightly slower than petrol, which may result in a minor drop in performance or increased consumption. Moreover, autogas parameters can be different depending on the propane-to-butane ratio – this varies by season as well. These problems are solved by STAG TAP-03. The unit forces an advance angle change to improve the effectiveness of air and fuel mixture combustion. The effect of using TAP is better performance (approx. 1-2%) and a noticeable consumption reduction (3 to 10%), which leads to lower exhaust emissions.

It transpires  that system assisting devices can bring more savings than usual. 14.07.2015

Autogas in winter

The gas system helps to reduce car operating costs significantly. In winter, gas-driven cars require special care. Here are our most important recommendations...
Winter, particularly its low ambient temperature, has a huge impact on the operation of the car. Apart from typical recommendations, like using winter tires or battery checks, in gas-fueled cars it is good to change the filters, especially fuel filters, and the best option is to make a periodic inspection of the whole vehicle. Autogas system inspections should be performed by specialized personnel.

Start the engine on petrol

If the car is equipped with an autogas system, it is recommended to start the engine on petrol. This reduces the wear and tear of the reducer (vaporizer) and flushes the system with petrol. When the ambient temperature drops down to -3OC, the temperature inside a cold reducer is -10OC. Currently, the European market offers membrane reducers provided with levers with rubber elements. The membranes and rubber elements become harder at low temperatures and wear faster in operation.

Most of the modern systems (generation 2 and 4) are equipped with temperature probes which have been installed on the reducers to enable the switch from petrol to gas fuel to be performed automatically. For example, the 2-generation systems, i.e. those designed for cars with Lambda probes and catalysts, particularly ones that are more advanced (Nicolaus, Leonardo, etc.) work with the temperature probe installed on the reducer. When the switch button is pressed to set the system in the GAS mode, the switching from petrol to gas is automatic, but only when the required temperature of the reducer has been reached and on the condition that all other requirements for switching have been met (rpm speed of the crankshaft, correct voltage reading of the throttle position sensor), depending on the applied fueling system configuration.

In this type of system, the driver does not need to pay attention to the temperature of the engine, as the electronic components determine the optimum moment for switching to autogas. Unfortunately, not all 2-generation systems are compatible with the temperature probe, which should be taken into account when selecting a system.

In the gas injection systems - 4th generation – temperature sensors are implemented as a standard: here the temperature is important not only when switching from petrol, but also during gas-fueled operation. Many gas injection systems are equipped with an additional temperature probe which has been installed in the injector line to ensure the constant correction of gas dosing for the required energy at variable temperatures.

In practice, sometimes there are technical problems with starting the engine on petrol. In an emergency situation, and also in winter, the engine can be started on gas, but due to the wear this has on the reducer, cold operation on gas should be avoided at low temperatures. After starting a cold engine on gas, let the car idle for a few minutes before driving, in order to warm the engine to at least 40OC. The engine warm-up preheats the antifreeze liquid that flows to the reducer and provides the heat energy which is required to vaporize the gas at the first vaporization stage.

By not burdening the cold engine unduly, we can ensure that the reducer is exposed to low temperatures only for a short time after the engine start. While the engine does not need much fuel on idle, its vaporization heat will not be high and the reducer will quickly warm up together with the engine unit.

Watch the quality of gas fuel

Clean gas is particularly important in winter. Low ambient temperatures result in lower pressure inside the gas tank. The ratio of propane to butane in the LPG mixture influences the pressure significantly. The lower the propane content, the lower the pressure.'

The user can observe reduced performance of an engine fueled with gas or a drop in pressure causing the fuel to switch from gas to petrol automatically (in gas injection systems). The effect of this is similar to that of an empty tank.

Care about your car

Keeping your filters clean - both on the reducer inlet side and further down the line, e.g. vapor phase filter in the gas injection systems - is an important recommendation for all users of gas-powered cars. This will eliminate unexpected issues if the temperature suddenly drops. Fortunately, LPG does not freeze in the tank or lines, even at very low temperatures. The key is to ensure the correct pressure and correct amount of heat delivered by the reducer (coming from the engine cooling circuit) to vaporize the liquid LPG (kept in the tank) to the vapor phase (delivered to the engine). Failure-free operation at low temperatures depends largely on the good technical condition of the vehicle.

Guidelines for users of gas-fueled cars in winter:

  • start a cold engine on petrol
  • use an antifreeze liquid in the engine cooling system
  • replace gas filters every 15k km
  • replace the air filter as specified by car manufacturer
  • keep the ignition system in good condition (HT cables, spark plugs)
  • use only high-quality gas 15.07.2015

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