Diesel generators are valuable machines that produce electricity by burning diesel fuel. Through combustion, they convert most of the chemical energy in diesel fuel into mechanical energy. The mechanical energy then turns the generator shaft, which, in turn, induces electrons within the system to produce an electric current.
They are incredibly popular among homeowners and even commercial facilities owing to diesel’s high energy output. Additionally, diesel, unlike natural gas generators, is portable.
If you’re considering purchasing a diesel generator for your home or business, this guide will help you understand a few things to make an informed decision.
What’s a Diesel Generator?
A diesel generator combines a diesel engine and an electric generator (typically an alternator) to generate electricity. It operates slightly differently from other generators. However, like any other fuel generator, the diesel engine burns fuel to produce the mechanical energy necessary to power the alternator.
Diesel generators are often used for standby and prime power. For instance, many contractors use diesel generators for prime power in remote regions with no electricity. You can also use it for backup purposes in case of a grid failure.
How Does a Diesel Generator Work?
The overall process is fairly straightforward. Assuming that you’ve filled up the diesel generator tank with quality diesel fuel, the following happens when you start the generator;
- Air is blown into the generator until it’s compressed.
- Fuel is injected into the diesel engine.
- The combination of compressed air and diesel fuel causes ignition.
- Combustion starts within the diesel engine.
- The resulting combustion and expansion actuate a piston system within the generator.
- The piston movement causes the engine shaft to turn at high speed.
- The turning shafts turn the rotor, one of the two main components of the alternator.
- The turning alternator creates an electromagnetic field.
- Passing the electromagnetic field through the stator (the second principal component of the alternator) produces an electron flow. An electron flow is known as an electric current.
- The direct electric current (DC) is harnessed and converted to a more efficient alternating current (AC), which is passed to the control panel and ultimately to your appliances, sometimes via an inverter.
Essentially, that’s how a diesel, and most other fossil-fuel generators, works. However, as we mentioned earlier, the process is slightly different for diesel generators, with the differences mainly manifested in the diesel engine.
How the Diesel Engine Works
Unlike the gasoline engine that relies on an electric spark, a diesel engine is an internal combustion engine that relies on air compression to generate heat.
The standard diesel engine operates on either a two-stroke or four-stroke cycle. However, unlike the gasoline engine, it only induces air into the combustion in the intake stroke. The engine compresses the air inside the cylinder to such a high degree that it ignites spontaneously when atomized diesel fuel is injected into the combustion chamber. Many diesel engines use a compression ratio of 15:1 or 23:1, causing the temperature within the chamber to rise sharply.
Diesel fuel is injected into the combustion chamber at the top of the compression stroke, right before combustion. It’s typically at a temperature higher than the auto-ignition temperature. Thus, it combusts spontaneously when it reacts with oxygen in the compressed air.
Actually, the intense heat first vaporizes the fine diesel fuel droplets, then burns the fuel until all the droplets are burnt.
The fuel is dispersed unevenly, creating what’s known as a heterogenous air-fuel mixture. This makes it possible to control the torque (the force to which the engine shaft is subjected) by manipulating the air-fuel ratio. This is also different from other fossil-fuel engines that rely on “throttling.” Rather than regulate the amount of air entering the combustion chamber, the diesel engine regulates the fuel injected into the chamber.
Combustion occurs at a relatively constant pressure throughout the initial part of the power stroke. However, when the vapor reaches the ignition point, it causes an abrupt pressure increase above the piston, causing it to descend. The expansion of the combustion gases at the end of the combustion process further forces the piston downward, supplying power to the crankshaft.
The crankshaft then rotates and turns the generator engine (alternator), producing electric current and ultimately stable electricity. The process keeps running, in the same cycle, to maintain the electricity supply.
Advantages of Diesel Engine Generators
Diesel engine generators are popular for many reasons, including efficiency and dual-fuel capabilities. Here’s why you should consider getting one;
1. Extremely efficient
Maybe that’s not exactly true, as most diesel engines are under 75% efficient. Indeed, in his essay, Theory and Construction of a Rational Heat Motor, Rudolf Diesel says that the practical efficiency of a diesel engine is between 43.2% and 50.4%. However, diesel engines are still, by far, the most efficient of all combustion engines.
The high efficiency is due to direct fuel injection into the chamber, elimination of intake air restrictions, and the absence of an intake manifold vacuum.
2. Highly versatile
Diesel engines can use various fuels, including several fuel oils, with advantages over petrol and gasoline. This allows users to enjoy lower fuel costs, good lubrication properties, and reduced fire risk.
For instance, biodiesel, an easily synthesized, non-petroleum-based product, can run in most diesel engines with no issues. Meanwhile, gas and petrol engines must be modified to run synthetic fuels.
3. Excellent exhaust characteristics
If you’re concerned about your carbon footprint, you’ll be glad to know that diesel engines have excellent exhaust emissions behavior. Diesel engine exhaust contains very few hydrocarbons and carbon monoxide.
For instance, pre-combustion chamber injection diesel engines only emit 50% of Otto cycle engines when operating under full load. In total, diesel engines emit under a tenth of the pollutants and less carbon dioxide than gas and petrol engines.
4. Easily adapt to damp conditions
You must have realized that fossil fuel engines perform very poorly in damp conditions. The electrical ignition system often causes this. Many electrical systems short circuit in damp conditions, causing what’s known as a “hard start” in cars.
Diesel engines are different as they rely exclusively on air compression to ignite the engine. The absence of a separate electrical ignition system means that it remains reliable even in damp conditions.
Diesel Generator Downsides
Unfortunately, diesel generators aren’t without downsides. The following are the main challenges associated with diesel engine generators;
1. The high price of diesel
Diesel prices are always higher than gas, petrol, natural gas, propane, and other fossil fuels. Why? Because the materials needed to produce diesel are not as abundant as other fuels. Additionally, diesel packs more raw energy per gallon than all the other fuels. Currently, gas retails at around $3.192, while diesel is priced at $3.305.
2. High initial costs
The other challenge with diesel engines, including diesel generators, is a high initial investment. Here, the reason is the engine design. Diesel engine designs are slightly different from other fossil fuel engines. The engines are heavier to handle the high compression ratios. Installing a diesel generator is also more expensive than a comparable petrol model.
Top Considerations When Shopping for a Diesel Generator
If you’ve read the pros and cons and still feel that a diesel generator is the perfect solution to your power requirements, the next step is to pick the right unit. Consider the following;
How much power do you need? To find out, list down all your appliances and devices and add their running power and starting power separately. Then add the two figures. You need a generator about 20% more than the final figure. For instance, if you determine that you need 10,000 watts from your backup generator, consider purchasing a 12,000-watt unit.
Diesel generators are available for single-phase and three-phase connections. This can help you select items to power when the power goes out to save on fuel costs. However, you can only use a phase system that matches your home’s wiring. So, find out if your home has a single-phase or three-phase system and buy the appropriate generator.
3. Fuel consumption rate
How much fuel does the generator consume per hour? The rate from one unit to the next, depending on the engine efficiency. For instance, although standard generators consume 1.4 liters of diesel to generate a kilowatt of electricity, some consume way less. Just keep in mind that increased efficiency often means a higher purchase price.
4. Control/power management systems
The two main things to consider here are the automatic power switch (ATS) and a power management system. The ATS automatically transfers your home circuitry to the generator whenever there’s a grid outage, saving you from having to transfer the load and switch ON the generator manually. Meanwhile, a power management system optimizes fuel consumption and generator performance depending on demand.
5. Noise output
Unfortunately, diesel generators are some of the noisiest power generators. The majority produce over 60 decibels when running, which can present many challenges if the generator is nearby. So, make sure to check the noise levels before taking home the generator. If your application requires very low noise levels, such as a home office, it would be better to compromise power for a 55-decibel unit or lower.
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That’s everything you need to know about diesel generators. However, make sure to properly maintain the unit for optimal operation and a long life. The diesel generator requires regular checks to ensure everything is running smoothly and a professional tune-up every 250-500 hours to keep it in top shape for a long time.