The choice of natural gas engine fuel today has become a strategic decision for many car owners seeking to save on operating a vehicle. The market offers two main options: compressed natural gas (methane) and liquefied petroleum gas (propane-butane mixture). Although both types of fuel provide significant cost savings compared to gasoline, their physical properties and storage conditions are fundamentally different.
Many drivers mistakenly believe that the difference is only in the octane number or the price at the gas station. In fact, chemical composition dictates completely different requirements for cylinders, supply systems, and even safety during operation. Understanding these nuances will help you avoid costly mistakes when converting your car.
In this article, we will analyze in detail the technical and operational characteristics of both types of fuel so that you can make an informed decision.
Physical properties and storage methods
The fundamental difference lies in the state of aggregation during storage. Propane (mixed with butane) is stored in a liquefied state under relatively low pressure, which depends on the ambient temperature. Typically this pressure ranges from 1.2 to 1.6 MPa. This allows large volumes of fuel in the liquid phase to be pumped into the cylinder.
Unlike him, methane does not turn into a liquid state at ordinary temperatures, no matter how much pressure we create (the critical temperature of methane is -82 degrees Celsius). Therefore, it is stored in compressed form under colossal pressure of 20–25 MPa. This requires the use of special cylinders that can withstand such loads without deformation.
Due to the difference in storage density, the volume of methane cylinders must be significantly larger to provide a comparable range. Propane cylinders more compact and lighter with the same energy reserve, which makes them more attractive for passenger cars with limited luggage space.
- ⛽ Methane is lighter than air: when leaked, it instantly evaporates upward, without forming explosive accumulations near the ground.
- 🛢️ Propane is heavier than air: if depressurized, it spreads along the bottom, filling holes and basements, which increases the risk of ignition.
- 💨 The energy density of methane is lower, so a larger volume of it is required to cover the same distance.
It is worth noting that octane number methane is higher (about 105-110 units) than propane (100-105 units). This allows engines running on methane to operate more steadily and with less risk of detonation, especially in high-speed modes.
Equipment and cost of installing gas equipment
The cost of re-equipping a car is one of the key selection factors. Complete set of gas cylinder equipment (GBO) for methane costs significantly more. This is due to the need to use expensive multi-stage compressors at gas stations and the high-pressure cylinders themselves, which are produced using more complex technologies.
Equipment for propane-butane cheaper and more accessible. The market is saturated with offers from various manufacturers, and gas stations themselves are found at every turn. The standard set includes a gearbox, injectors, an electronic control unit and a cylinder, which can be cylindrical or toroidal (for installation in the spare wheel niche).
⚠️ Attention: When installing methane equipment, the weight of the cylinders can reach 80-100 kg or more. This significantly affects the vehicle's weight distribution and load capacity, which is critical for light commercial vans and compact cars.
Modern 4th and 5th generation systems make it possible to integrate gas equipment so that switching between fuel types occurs unnoticed by the driver. Electronics corrects itself fuel mixture composition depending on engine load and temperature.
It is important to consider that methane systems require more skilled installation and regular complex checking of the tightness of connections. Propane systems are more forgiving in this regard (forgive minor mistakes), although they require no less attention to rubber hoses, which dry out over time.
Economic efficiency and fuel consumption
When calculating the payback, it is necessary to look not only at the price of a liter at the gas station, but also at the actual consumption. Methane It is approximately 2-2.5 times cheaper than propane, but its energy density is lower. This means that to perform the same work, the engine will need more cubic meters of methane than liters of propane.
Propane consumption is usually 10-15% higher than gasoline, while methane consumption in terms of gasoline equivalent can be 20-25% higher in volume, but significantly lower in value in monetary terms. For commercial vehicles with high mileage methane remains the uncontested leader in net profit.
☑️ Factors for calculating the payback of gas equipment
However, for a private car with a mileage of up to 20 thousand kilometers per year, the difference may not be so obvious. If you live in an area where the network methane gas stations is poorly developed, time spent searching for fuel can offset all financial benefits.
When calculating the payback, take into account not only the price of gas, but also the possible reduction in engine life. Methane dries out the combustion chamber, which requires more frequent replacement of spark plugs and valve adjustments.
Operational safety and environmental friendliness
The issue of safety often becomes decisive. As mentioned earlier, methane is lighter than air and simply evaporates when leaked, without creating a concentration of an explosive mixture in a confined space (for example, in a garage). Propane, being heavier than air, accumulates in low areas, which makes its leakage more insidious and dangerous.
On the other hand, the strength of methane cylinders is extremely high. They pass bulletproof tests and are able to withstand pressures many times higher than operating pressure. It is extremely difficult to destroy such a cylinder in an accident. Propane cylinders are also equipped with safety valves that relieve pressure in case of fire, but their body is less resistant to mechanical damage.
⚠️ Attention: Operating a vehicle with gas equipment requires regular inspection of the cylinders. For propane this is usually every 2 years, for methane - every 5 years (depending on the material of the cylinder and the legislation of the country). Ignoring this rule is life-threatening.
From an environmental point of view methane is the cleanest type of hydrocarbon fuel. When it burns, a minimal amount of harmful substances is formed, and virtually no soot is released. This extends the life of the engine oil and reduces wear on the cylinder-piston group.
Comparison table of characteristics
For ease of understanding, we will summarize the main parameters in a single table. This will help you quickly navigate the key differences.
| Characteristics | Methane (CNG) | Propane-Butane (LPG) |
|---|---|---|
| Cylinder pressure | 20–25 MPa | 1.2–1.6 MPa |
| Physical state | Gaseous (compressed) | Liquid (liquefied) |
| Octane number | 105–110 | 100–105 |
| Equipment weight | High (heavy cylinders) | Medium/Low |
| Fuel cost | Low | Average |
As can be seen from the table, technical differences significant. The choice between them is always a compromise between initial investment, range and infrastructure availability.
Impact on engine life
Gaseous fuel has its own combustion characteristics. It does not wash away the oil film from the cylinder walls, as gasoline does, which theoretically should extend the life of the engine. However methane has a higher combustion temperature, which can lead to overheating of valves and seats if the engine is not specifically adapted to run on gas.
Propane is softer in this regard, but if configured incorrectly gas injectors can cause “popping” in the intake manifold, which is dangerous for plastic intake elements and sensors. Modern multipoint injection systems have reduced this risk to a minimum.
Effect on oil
When running on gas, the oil oxidizes faster due to the high combustion temperature. It is recommended to reduce oil change intervals by 20-30% and use gas specifications (LPG/CNG).
Owners of older cars with hydraulic valve clearance adjusters should be careful: gas requires more frequent adjustment of the thermal clearances, since it does not contain substances that lubricate the valve seats, unlike leaded gasoline of the past (although gasoline is now also unleaded, but the additives in the gas may differ).
Where and how to refuel
Infrastructure is the Achilles heel of natural gas engine fuel. If propane gas stations can be found in almost any large settlement and on many highways, then the network methane gas stations (CNG filling station) is unevenly developed. In the central regions their density is high, but when planning long trips through a remote province, the route must be carefully planned.
Refilling with methane takes longer due to high pressure and the need to heat the gas before entering the cylinder (to avoid hypothermia). You can refuel with propane faster; the process is not much different from refueling with gasoline.
⚠️ Attention: Do not try to fill a full tank “to capacity”. For propane, there is a rule of 85% of the volume (the rest is a gas cushion for expansion of the liquid when heated). Overfilling can lead to an emergency release of pressure through the valve on a hot day.
It is also worth considering seasonality. In winter in propane-butane mixture the proportion of butane may increase, which evaporates less well at low temperatures, which leads to difficulties starting the engine on gas. Methane does not have this disadvantage, since it is always in a gaseous state.
The choice between methane and propane depends on your annual mileage: up to 30,000 km, propane is more profitable due to the cheapness of the equipment; over 50,000 km, methane will pay for itself faster due to the low price of fuel.
Summary of fuel selection
To sum it up, there is no universal answer. For taxi drivers, courier services and truck drivers who travel hundreds of kilometers every day, methane is the uncontested leader in economics. The high initial cost of the equipment pays off in 6-10 months of active driving.
For private use, country trips and moderate urban use propane seems like a more rational choice. It is easier to maintain, does not steal so much space in the trunk and forgives the lack of specialized gas stations near your home.
The main thing is to remember that the installation of any gas equipment should be carried out only in certified centers with the issuance of all the necessary documents for registering changes with the traffic police. Homemade taps and the use of used cylinders with expired service life are a direct threat to your life and the lives of others.
Keep receipts from gas stations. In some regions and for certain categories of owners (legal entities, disabled people), there are programs for compensation or subsidies for the purchase of gas, where confirmation of the volume of refueling is required.
Is it possible to switch the car back to gasoline?
Yes, it's possible. The design of the gas equipment allows you to dismantle the equipment and return the car to factory settings. However, there may be changes left in the engine (for example, installed valve spacers or changed ECU settings) that it is advisable to neutralize. You will also need to go through the procedure of registering a reverse design change with the traffic police.
Is it true that gas explodes more often than gasoline?
Statistics show that gas equipment ignites less often than gasoline equipment. Gas cylinders are stronger than gas tanks, and safety systems (valves, electromagnetic cut-offs) are triggered instantly if the line breaks. Most accidents are associated with unskilled installation or the use of defective components.
Will engine power decrease on gas?
A slight drop in power (by 3-7%) is indeed observed, since the gas occupies part of the volume of the combustion chamber, displacing air. However, in practice, in urban driving, this is almost unnoticeable. Dynamic characteristics are maintained at an acceptable level, especially when using modern 4th generation systems with injection timing correction.
Which gas is better in winter?
Methane behaves more stable at low temperatures, since it does not depend on the evaporation of the mixture components. Propane-butane in winter requires a larger proportion of propane in the mixture, otherwise the engine may stall or not start. However, modern reducer evaporators effectively heat the gas, minimizing this problem.
Do I need to warm up the engine before switching to gas?
Yes, this is a mandatory requirement for most systems. Switching to gas occurs automatically after the coolant warms up to a certain temperature (usually 30-40 degrees). Starting and operating a cold engine is possible only with gasoline to ensure lubrication and correct thermal conditions of the gearbox.