Dual Fuel and LPG Generators Explained

Most portable generators are designed to operate on a single fuel, such as petrol or diesel. However, dual-fuel and LPG generators provide additional flexibility by allowing the user to generate electricity using more than one fuel source.

A dual-fuel generator will commonly operate on both petrol and liquefied petroleum gas, usually referred to as LPG. Some larger standby generators may also be designed to operate on LPG or mains natural gas.

Having more than one fuel option can be valuable during a power cut, on a remote worksite or in any situation where one type of fuel may be difficult to obtain. However, dual-fuel generators also have different performance, storage and installation considerations compared with conventional petrol generators.

This guide explains how dual-fuel and LPG generators work, their main benefits and limitations, and how to decide whether one is suitable for your needs.

What Is a Dual-Fuel Generator?

A dual-fuel generator is an engine-driven generator that can operate using either of two approved fuels.

The most common combination is:

• Petrol
• LPG, such as propane supplied from a suitable gas cylinder

The generator normally has a conventional petrol tank together with a gas inlet, regulator and fuel-selection control. Depending on the model, the operator may select the required fuel before starting or change fuel while the generator is running.

The exact changeover procedure varies between manufacturers. The operating manual should always be followed, as not every dual-fuel generator is designed to switch fuels under load.

Many portable dual-fuel models use an open-frame generator design, which provides easy access to the engine and components while helping to keep the generator relatively compact and portable.

What Is an LPG Generator?

An LPG generator is designed to produce electricity while running on liquefied petroleum gas. LPG is normally stored under pressure in a cylinder and supplied to the generator through an approved regulator and hose assembly.

In the UK, bottled LPG commonly includes propane and butane. Propane is generally preferred for generator use because it performs better at lower outdoor temperatures.

Some generators run exclusively on LPG, while dual-fuel models allow the operator to choose between LPG and petrol. Larger fixed standby generators may be designed to operate on LPG or natural gas rather than petrol.

How Does a Dual-Fuel Generator Work?

A conventional petrol generator mixes liquid petrol with air before the mixture enters the engine. An LPG system instead delivers gas through a regulator that controls pressure and supplies the correct amount of fuel to the engine.

On a dual-fuel generator, both systems are incorporated into the same machine. A selector valve or control determines which fuel reaches the engine.

A typical dual-fuel system includes:

• A built-in petrol tank
• A petrol fuel valve and carburettor
• An LPG connection
• A pressure regulator
• A fuel-selection control
• Fuel-specific starting instructions

The generator still produces electricity in the same way regardless of the chosen fuel. The engine turns the alternator, which produces the electrical output supplied through the generator sockets.

What Are the Benefits of a Dual-Fuel Generator?

Greater Fuel Flexibility

The main advantage is the ability to use whichever approved fuel is available.

During a widespread power cut, petrol stations may be closed or unable to operate their pumps. A stored LPG cylinder can provide an alternative fuel supply.

Similarly, if the LPG supply runs out, the generator may be able to continue operating using petrol.

Longer Combined Running Time

A dual-fuel generator can potentially provide a longer total operating time because it can use both the petrol in its tank and the gas available from an LPG cylinder.

The actual running time will depend on:

• The electrical load
• The petrol-tank capacity
• The size and fill level of the LPG cylinder
• The generator’s fuel-consumption rate
• Ambient temperature

Fuel should never be changed or replenished contrary to the manufacturer’s instructions.

Improved Fuel Storage

Petrol degrades during storage and can cause starting or carburettor problems when left in a generator for extended periods.

LPG does not deteriorate in the same way while it remains safely contained within a serviceable cylinder. This can make LPG useful for emergency-preparedness applications where the generator may remain unused for long periods.

Gas cylinders must still be stored, handled and inspected correctly.

Cleaner Engine Operation

LPG generally burns more cleanly than petrol and can leave fewer deposits within the engine and fuel system.

Potential benefits may include:

• Reduced carbon deposits
• Cleaner engine oil
• Less carburettor contamination
• Reduced petrol-related storage problems

This does not remove the need for routine servicing. Oil changes, air-filter maintenance, spark-plug checks and general inspections remain essential.

Convenient Emergency Backup

A dual-fuel generator can be useful for household or business backup because it reduces reliance on a single fuel.

It may be suitable for supporting essential equipment such as:

• Refrigerators and freezers
• Lighting
• Heating controls
• Communication equipment
• Small pumps
• Office equipment
• Selected tools and machinery

The generator must be correctly sized for both the running and starting requirements of the connected equipment.

What Are the Disadvantages of Dual-Fuel Generators?

Lower Output on LPG

Many dual-fuel generators produce slightly less power when operating on LPG than when operating on petrol.

For example, a generator advertised with a maximum petrol output may have a lower rated output when running on gas. This reduction varies by model and should be checked before purchase.

Generator sizing should be based on the output available from the fuel you expect to use, rather than assuming the petrol and LPG ratings are identical.

Additional Equipment

Using LPG requires suitable equipment, which may include:

• An approved gas cylinder
• The correct regulator
• A compatible hose
• Secure cylinder positioning
• Safe cylinder storage

Only components approved by the generator or equipment manufacturer should be used. Improvised fittings or incompatible regulators can create a serious gas-leak and fire risk.

More Complex Starting Procedures

The starting process may differ depending on whether the generator is using petrol or LPG.

A petrol engine may require the choke to be used, while LPG starting may involve opening the cylinder valve, priming the gas system or using a different choke position.

Users should become familiar with both procedures before the generator is needed during an emergency.

Gas Availability and Cylinder Management

LPG cylinders must be refilled or exchanged through a suitable supplier. Availability may vary by location, especially during periods of high demand.

It is also important to know how much usable fuel remains in the cylinder. Unlike a petrol tank, the remaining gas level may not be immediately visible.

Cylinder weight, compatible level indicators or automatic changeover arrangements may help with fuel management.

Does an LPG Generator Produce Less Power?

In many cases, yes. A dual-fuel generator will often have separate petrol and LPG output ratings.

LPG contains less usable energy per unit of fuel supplied to the engine than petrol, which can lead to a modest reduction in engine and generator output.

The difference may be relatively small, but it becomes important when powering appliances or machinery with high starting currents.

Always check:

• The maximum output on petrol
• The rated continuous output on petrol
• The maximum output on LPG
• The rated continuous output on LPG

Do not size a generator using its maximum or surge output alone. The continuous rated output should be sufficient for the normal combined load.

Is LPG Cheaper Than Petrol for a Generator?

The relative running cost depends on current fuel prices, the generator’s efficiency and whether the LPG is purchased in refillable or exchange cylinders.

LPG may cost less per litre than petrol, but the generator may consume a greater volume of LPG to produce the same amount of electrical energy.

A meaningful comparison should consider:

• Fuel price
• Generator fuel consumption at the expected load
• Available electrical output on each fuel
• Cylinder rental, deposits or exchange charges
• The distance travelled to obtain fuel

For occasional emergency use, the storage life and availability of LPG may be more important than the lowest possible hourly operating cost.

How Long Will a Generator Run on an LPG Cylinder?

The running time depends on the cylinder size, the amount of LPG it contains and the generator’s load.

A generator powering a light load will generally run considerably longer than the same machine operating close to its rated output.

Manufacturer run-time figures should be treated as estimates because actual consumption is affected by:

• Electrical demand
• Engine condition
• Ambient temperature
• Fuel quality
• Regulator performance
• Cylinder pressure

In cold conditions, the cylinder may struggle to vaporise LPG quickly enough for a heavily loaded generator, even when some liquid fuel remains inside.

Can a Dual-Fuel Generator Switch Fuels While Running?

Some generators are designed to change between petrol and LPG while operating, while others must be stopped before the fuel is changed.

Never assume that live fuel switching is permitted. An incorrect changeover procedure may cause:

• Engine stalling
• Fuel leakage
• Backfiring
• Damage to the fuel system
• Unstable electrical output

Before changing fuels, reduce or disconnect the electrical load where required and follow the exact procedure in the operating manual.

Are LPG Generators Safer Than Petrol Generators?

Both fuels can be used safely when the generator is operated correctly, but each presents different hazards.

Petrol Risks

• Petrol vapour is highly flammable
• Spilled petrol can ignite on hot components
• Petrol can deteriorate during storage
• Fuel containers must be stored safely

LPG Risks

• Gas can escape from damaged or loose connections
• LPG is heavier than air and may collect in low areas
• Cylinders can become dangerous if exposed to fire or excessive heat
• Incorrect regulators or hoses may cause unsafe pressure

The generator and gas cylinder must always be operated outdoors in a well-ventilated position, away from ignition sources, doors, windows and air vents.

Carbon Monoxide and Ventilation

LPG may burn more cleanly than petrol, but an LPG generator still produces carbon monoxide.

Carbon monoxide is a colourless and odourless gas that can cause unconsciousness or death. No portable fuel-powered generator should be used inside:

• A house
• A garage
• A shed
• A workshop
• A tent
• A warehouse
• A partly enclosed area

Opening doors or windows does not make indoor generator use safe.

The generator should be positioned outdoors, well away from occupied buildings and any opening through which exhaust fumes could enter.

Carbon-monoxide alarms should be installed in nearby occupied buildings as an additional safety precaution.

How Should an LPG Cylinder Be Positioned?

The cylinder should be placed upright on a stable surface unless the cylinder and appliance are specifically designed for an alternative orientation.

It should be kept:

• Away from the generator exhaust
• Away from hot engine components
• Clear of direct impact or vehicle movement
• Outside enclosed or poorly ventilated areas
• Within the hose distance permitted by the manufacturer

The hose should not be stretched, trapped, kinked or allowed to contact sharp edges or hot surfaces.

Gas connections should be checked for leaks using an approved leak-detection method. A naked flame must never be used to check a gas connection.

Can You Use Butane Instead of Propane?

Only use the fuel specifically approved by the generator manufacturer.

Propane is generally more suitable for outdoor generator use because it continues to vaporise at lower temperatures. Butane may perform poorly in cold weather and may require a different regulator pressure.

A generator labelled for propane or LPG should not automatically be assumed to accept every gas cylinder or regulator type.

Dual-Fuel Generator Maintenance

Dual-fuel generators require the same basic maintenance as conventional petrol generators, together with inspection of the gas system.

Routine maintenance may include:

• Checking and changing the engine oil
• Cleaning or replacing the air filter
• Inspecting or replacing the spark plug
• Checking the petrol fuel system
• Inspecting the LPG hose and regulator
• Checking gas connections for damage
• Keeping ventilation openings clear
• Testing the generator under load
• Following the manufacturer’s service intervals

Even when the generator is normally operated on LPG, the petrol system should be maintained if the petrol option is expected to remain available.

Old petrol should not be allowed to remain indefinitely in the tank or carburettor.

Are Dual-Fuel Generators Suitable for Sensitive Electronics?

Conventional dual-fuel generators may be suitable for general appliances, lighting and tools, but the quality of the electrical output varies between models.

Where sensitive electronics, computers, televisions, audio equipment or battery chargers will be powered, an inverter generator may be preferable because it is designed to provide a stable electrical output with low waveform distortion.

Always check the generator’s voltage regulation, waveform quality and manufacturer recommendations before connecting sensitive equipment.

Who Should Consider a Dual-Fuel Generator?

A dual-fuel generator may be suitable for:

• Homeowners preparing for power cuts
• Businesses requiring temporary backup power
• Mobile catering and event operators
• Caravan and leisure users
• Remote workshops
• Agricultural users
• Tradespeople working away from mains electricity
• Anyone who values the security of two fuel options

A conventional petrol generator may remain the simpler choice for short, occasional use. For frequent heavy-duty operation, a diesel generator may provide better durability and fuel efficiency.

Where low operating noise is a priority, an enclosed silent generator may be more appropriate than an open-frame dual-fuel model.

Do You Need a Single-Phase or Three-Phase Generator?

Most portable dual-fuel generators provide a single-phase electrical supply and are intended for conventional tools, appliances, lighting and household backup requirements.

Commercial machinery, larger motors and industrial equipment may require a three-phase generator. Three-phase generators are designed to supply equipment operating from a 400V electrical system, although some models may also provide a 230V auxiliary supply.

Before purchasing a generator, check the voltage, phase and socket requirements of every item that will be connected. A three-phase generator should not be selected solely because it has a high power rating, as the available output may be distributed across its three phases.

What to Check Before Buying

Before choosing a dual-fuel or LPG generator, check:

• The petrol and LPG rated outputs
• The maximum starting output
• Whether the generator is single phase or three phase
• The required voltage
• The socket types and ratings
• The expected running time on each fuel
• The approved gas type
• Whether the regulator and hose are included
• The permitted cylinder sizes
• The generator noise level
• Whether an open-frame or silent design is more suitable
• The starting method
• The generator weight and portability
• The service and warranty requirements

It is particularly important to establish whether the quoted output applies to petrol, LPG or both. You should also confirm whether the generator provides the correct voltage and phase arrangement for the equipment being powered.

Dual-Fuel vs Petrol Generator

A petrol-only generator is usually simpler and may cost less to purchase. It may also provide a slightly higher maximum output than an equivalent generator running on LPG.

A dual-fuel generator offers greater flexibility, potentially longer combined running time and improved long-term fuel-storage options.

The better choice depends on whether simplicity, maximum power or fuel flexibility is most important for the intended application.

Dual-Fuel vs Diesel Generator

Dual-fuel petrol and LPG generators are often used for portable or occasional applications. Diesel generators are generally more suitable for prolonged, high-load and commercial use.

Compared with a dual-fuel model, a diesel generator may offer:

• Improved fuel efficiency under sustained load
• Longer engine life in heavy-duty applications
• Better suitability for prime-power use
• Larger fuel tanks on long-run models

However, diesel generators may be heavier, more expensive and noisier unless they are fitted with an acoustic enclosure.

Conclusion

Dual-fuel and LPG generators provide valuable flexibility by allowing electrical power to be produced without relying entirely on petrol.

LPG offers long storage life, cleaner combustion and a useful alternative fuel during an emergency. Petrol may provide slightly higher output and can be easier to obtain in some circumstances.

The best choice depends on the required electrical output, expected operating time, fuel availability and how frequently the generator will be used.

Before purchasing, compare the generator’s petrol and LPG outputs, check the approved cylinder and regulator requirements, and ensure the generator is appropriately sized for the connected equipment.

Whichever fuel is used, the generator must always be operated outdoors, maintained correctly and used in accordance with the manufacturer’s safety instructions.