Gasoline Generators: Everything You Need to Know

Gas generators are ubiquitous today, perhaps some of the most common generators. Indeed, if you’re shopping for a portable fossil-fuel generator, there’s a great chance you’ll bring home a gas-powered unit.

gasoline power generator

One of the reasons for their popularity is the affordability of gas. Gas is only slightly more expensive than diesel. However, it’s easier to use than diesel. Moreover, diesel engines are significantly more expensive. Gasoline is also easier to handle. 

So, given these advantages, should you opt for a gas model when shopping for a generator? to find out, you need to learn more about gas generators.

What’s a Gas Generator?

A gas generator is an electric power generator that runs on gasoline. This is different from diesel generators that run on diesel and propane generators that operate on liquified propane gas (LPG).

Gas engines incorporate gas engines, similar to the engines in standard gasoline cars, that burn gas to generate electricity. Generally, the engine produces a torque that drives a shaft connected to the generator’s alternator. Then a rotating coil inside the alternator creates an electromagnetic field that generates an electric current to power your appliances and devices.

It’s worth noting that some modern generators can handle more than one type of fuel. For instance, bi-fuel generators can run on two different fuels, while tri-fuel units can operate on three different fuel types, typically natural gas, propane, and gasoline. We usually classify these systems as multi-fuel generators to avoid unnecessary confusion when shopping. 

How Does a Gas Generator Work?

Gas generators comprise two main components, the gas engine, and the generator’s alternator. The engine handles the conversion of gasoline’s chemical energy into mechanical energy, while the alternator converts mechanical energy from the engine into electrical energy to power your home or equipment.

How the Gas Generator Works

Most fossil fuel engines are internal combustion engines. This means that they release energy from a fuel and air mixture that happens within a combustion chamber.

However, there are two broad categories of internal combustion engines, i.e., Spark Ignition (SI) engines, and Compression Ignition (CI) engines. Gas generators are typically spark-ignition engines, whereas diesel units are compression ignition systems.

Compression engines work on the principle of the diesel cycle or constant pressure heat addition cycle. Fuel ignition occurs due to the high temperature of compressed air inside the combustion chamber. Therefore, spark plugs aren’t necessary. Air compression to such high temperatures is made possible because CI engines first introduce air into the combustion chamber with fuel (diesel) injected right at the end of the compression, immediately before combustion, at high pressure.

This isn’t possible with spark ignition systems as the fuel is mixed with air, and the two are introduced into the combustion chamber together. Compressing a mixture of air and fossil fuel to very high temperatures can cause knocks that may damage the engine. This explains why the compression ratios in diesel engines are as high as 22:1, whereas, in gas engines, it’s 6-10:1 at most.

So, how does an SI engine work? Well, spark-ignition engines operate on the otto cycle principle that uses a spark plug to ignite the engine.

The standard otto engine comprises many components. However, the main parts that generate motion are as follows;

  • An inlet valve: Is a small valve through which a mixture of air and fuel enters the engine. The valve, thus, regulates the rate at which fuel + air mixture enters the engine.
  • The exhaust valve: Is the valve through which exhaust gases exit the engine. Exhaust gases are expelled from the engine in the power stroke.
  • The spark plug: The spark plug is responsible for generating the spark that ignites the compressed air + fuel mixture. Ignition occurs at the end of the compression stroke.
  • Piston: The piston is a tubular component fitted into the engine cylinder that makes reciprocating movements and transfers rotary motion to the output shaft.
  • Cylinder: The cylinder system comprises the cylinder block and the cylinders themselves. The block is solid metal, usually cast iron, that forms the main body of the engine. It provides the supporting structure and holds the other components together. Meanwhile, the cylinders are cylindrical vessels in which the piston makes reciprocating motions.
  • Connecting rod: This metal rod connects the piston to the crankshaft, thus transmitting power from the piston to the crankshaft.
  • The crankshaft: Encased in the crankcase, the crankshaft converts the piston’s reciprocating motion to rotary motion. Bearings, a pair of crank arms, and balancing wheels help provide balance while reducing friction.

The Four Piston Strokes

As we’ve mentioned, fuel is mixed with air before it enters the combustion chamber. The rest of the process happens in four stages, or four strokes of the engine;

1. The suction stroke

The piston moves downward, opening the gas valve. This allows the air + gas mixture to enter the combustion chamber from the carburetor. The exhaust valve remains closed during the suction cycle.

2. The compression stroke

Here, the piston moves upward and compresses the air + fuel mixture above it. The compression stroke ends when the piston moves Top Dead Center (TDC) at the very top of its stroke. Both valves remain closed during this process.

3. The power stroke

This is where the magic happens. At the end of the compression stroke, the temperature of the gas + air mixture is high enough to ignite the spark plug. When the spark ignites, it causes the fuel + air mixture to combust, a process that generates a significant expansion. The expansion causes a thrust force that pushes the piston downward rapidly, causing the crankshaft to rotate. It’s called the power stroke because it’s where mechanical power is generated. Both the inlet and outlet valves remain closed.

4. The exhaust stroke

In the exhaust stroke, the piston moves upward as the pressure within the combustion chamber falls. Then, with the inlet valve closed, it pushes burnt/exhaust gases out of the cylinder through the now open exhaust valve as it moves up.

Once the exhaust stroke completes, the suction process restarts the process, which goes on and on until you stop the engine.

At the Alternator

Once the engine shaft begins to turn, the rest of the process works like any other fossil fuel generator. The shaft connects to the alternator’s rotor, a mobile section of the alternator. Therefore, when the shaft turns, the rotor turns too. The faster the engine shaft turns, the faster the rotor turns.

The rotor is located within a magnetic field provided by the stator, the second principal component of the alternator. Since the rotor comprises many conductor-wire coils, the motion within the magnetic field naturally yields an electromagnetic field.

The alternator harnesses the electron flow within the field. Then, it directs the electrons through copper wires to create an electric current. The current is then sent to the control panel, where you can tap it to power your appliances.

Gasoline Generator Advantages

Gasoline generators are advantageous over diesel and other fossil fuel generators in many ways, including;

  • Gas is readily available: Gas is perhaps the most widely available fossil fuel, notably because 70% of motor vehicles run on it.
  • Gas burns cleanly: Only diesel burns more cleanly than gasoline. It’s better than both propane and natural gas and produces more energy (BTUs) per unit.
  • Gas engines are very light: This is especially when comparing gas with diesel. Diesel engines are bulkier and more complex.
  • Easier maintenance: Gasoline engines are the simplest, thus easiest to maintain, of all fossil fuel generators. Diesel generators, for instance, are a lot more expensive to repair because of the complexity.

Gasoline Generator Disadvantages

  • Poor longevity: Gas engines don’t last long compared to diesel engines. The gas combustion chamber is more susceptible to high compression ratios.
  • Short storage life: Of all fossil fuels, gasoline has the shortest “life expectancy.” Without proper care, using a stabilizer, your gasoline will “go bad” within weeks. Even with a stabilizer, it can only last six months at most. Meanwhile, diesel can last more than ten years with a stabilizer, while propane and natural gas pretty much don’t go bad.

Making the Right Choice

If you ultimately decide to purchase a gasoline generator, make sure to pick the right one for the application. Specifically, consider the following factors;

  • Buy the right size (wattage): Determine your power needs and choose a large enough generator to meet those needs.
  • Make sure it’s portable enough: Check for handles and wheels. Also, check for feet. However, if you’re buying a large, permanently fixed model, hire a professional for the installation.
  • Consider run time (in hours): How long can it last on a full tank? This directly determines how often you need to refill the tank.
  • Select a great band: You want to go with a brand that offers exceptional customer support and worthwhile warranties.
  • Shop within budget: The most expensive products aren’t necessarily the best. To find value, you need to shop around.


That’s all you need to know about gasoline generators. We want to stress the need to test the unit before purchasing. It’s the only way to prove that the unit works as the manufacturer (and salesperson) claims. So, if you’re buying online, consider sellers who allow returns after a specified period if the equipment doesn’t work to specification.

Gasoline Generators: Everything You Need to Know

Carter Brooks

I'm Carter Brooks, an expert in portable generators with a background in Mechanical Engineering. My experience spans from working in the manufacturing industry, where I gained hands-on knowledge of various machinery, to a focused career in blogging about portable generators. I combine my technical expertise with real-world experience, garnered from numerous camping trips and outdoor adventures, to provide in-depth reviews and practical advice. My blog is dedicated to helping consumers understand and choose the best generators for their needs, emphasizing both efficiency and environmental impact.

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