Introduction: Envisioning the Future of Forklift Power Systems

I am currently a sophomore at Adlai E. Stevenson High School in Lincolnshire, Illinois.

Forklifts are an integral part of the business industry. They facilitate the movement of various items that are extremely large and heavy and with great speed. The heart of these machines is their power systems, which allow them to move both themselves and the objects they carry. This instructable focuses on these power systems: each's advantages and disadvantages, along with what value they hold in the future.

Step 1: What Options Currently Exist?

There exist many different power sources for forklifts, with the majority of modern forklifts running on either a liquid fuel source, a liquefied gas, a compressed gas, or off of a source that provides electric power. The following section discusses these sources, and some potential new ones, as long as some advantages and disadvantages. I also try to link both my sources and further reading and investigation sections.

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Combustion Engines:

Combustion engines, as the name implies, are combust fuels to extract their energy. The basic operation principle is as follows:

  • The fuel, along with some air, is injected into a hollow cylinder.
  • Then, a piston comes up, compressing the fuel and air mixture.
  • Finally, the compressed air and fuel mixture are ignited, and a large force is exerted on the piston. This in turn causes the piston to accelerate, giving it kinetic energy. The piston's motion is used to drive the output of the engine.

In this way, the Potential Chemical Energy of the fuel is converted into Kinetic Energy, which can be used to drive the various systems on the forklift. Here are some pros & cons of combustion engines:

Pros of Combustion Engines:

  • Can run on a variety of fuels
  • Very reliable
  • Cheaper to purchase
  • Higher Energy Density than other common engine types (e.g. Electric)
  • Quick and Easy to refuel

Cons of Combustion Engines:

  • Mechanically Complex
  • Loud
  • Produce Noxious gasses
  • Tend to Vibrate
  • Fuels prices add up over time

  • Additional operator training

  • Less maneuverable than electric counterparts (Greater stopping distance, slower acceleration, etc.).

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Combustion Fuels:

Combustion Engines require Combustion fuels to operate. Combustion Engines is that they can accept a large number of different fuels, with each having its advantages and disadvantages. Here are some various combustion fuel types often used in forklifts:

Liquid Fuels:

The primary liquid fuels used in combustion engine forklifts are Gasoline and Diesel, which are both petroleum distillates. Due to society's reliance on these fuels, primarily from the automotive industry, these fuels are very easy to get and are reasonably priced. These fuels, being liquids, are very easy to store and transport. They are also very energy-dense, having around ~50MJ/kg & ~30MJ/L (Every kilogram of Gasoline/Diesel has 50 Megajoules, and every liter of Gasoline/Diesel has 30 Megajoules. Higher is better).

Compressed Gas Fuels:

Another frequently used Combustion Engine fuel type is Compressed Gas Fuel. Gasses also can store lots of Potential Chemical Energy, and they can be relatively efficiently be stored in pressure tanks. Some common examples are Propane, Butane, Methane, and more. Their energy density is lower than that of Liquid Fuels (~50MJ/kg & ~10MJ/L), and also requires heavy metal containers to store these fuels under pressure. Compressed Gas Fuel based forklifts tend to be the most cost-effective and widely available, as they are the most common design, but are more difficult to refuel, due to compressed gasses being less available.

Liquid Gas Fuels:

Liquid Gas Fuels are a subset of Compressed Gas Fuels, in which energy-rich gasses are compressed and cooled to the point they liquify. Liquid gas fuels have a specific energy density of ~50 MJ/kg, and an energy density of ~25 MJ/L, which is a significant improvement over Compressed Gas Fuels. The most common Liquid Gas Fuel type is Methane.

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The energy densities of various combustion fuels are shown in figure 1.

Electric Power:

Other than combustion engines, all other forklifts use some sort of electric power system. In an electric motor, a voltage is coupled either with a mechanical or electronic device which creates a changing magnetic field, which causes embedded magnets within the motor to move. A motor requires a voltage source to operate, of which some are discussed in the following section:

Batteries:

A battery is a device that stores electrical energy through some sort of chemical process. There exist many different battery types, all with varying construction, rechargeability, durability, safety, weight, energy densities, etc. Figure 2 shows various batteries' energy densities (Source). Note that 1 Wh is equal to 0.0036 MJ. The most common battery used are lithium-ion batteries, which have some of the highest energy densities of ~1-2 MJ/kg and about ~1-2 MJ/L. Note how little this is in comparison to combustibles, which have an energy density that can be over 25-50 times greater.

Many newly sold forklifts are electric, but their issues do the show. They are heavier than their combustion counterparts, require extra space, wear with time, require and require extra space. Charging a battery forces ions from the cathode to the anode; using the battery reverses the flow. Over time, this process wears out the cathode, which results in reduced capacity. On the other hand, they are much cheaper to refuel and come with many benefits of not using a combustion engine: no vibrations, no noxious gasses, greater maneuverability, etc.

Hydrogen (Fuel cell):

Hydrogen is the first element on the periodic table and is an extremely flammable and energy-dense gas (energy density of ~120MJ/kg, and ~10MJ/L). Although it can be used as a combustion fuel, it can also be used as a source of electricity. There exists a technology called a Proton-exchange membrane fuel cell, which can very efficiently oxidize hydrogen, and release the potential chemical energy as electricity. Not only are these fuel cells extremely efficient, they only release one thing as a by-product: water (H2O). This brings us to the next advantage of hydrogen, that it can be readily produced. When you subject water to an electric current, the water is broken down into hydrogen and oxygen, the two components needed for a hydrogen fuel cell.

This technology is not very widespread, with only a small amount of forklifts in production that use hydrogen fuel cells.

Other/Exotic:

This section focuses on technologies that can produce either direct motion, or produce some other energy type that can be used to drive a forklift.

Nuclear:

A fission reactor, which can use either uranium, plutonium, or thorium could be a candidate for forklift power systems. In many space applications, RTGs, a form of nuclear reactors, are used due to their long life span. Forklifts demand significantly more power than what an RTG can produce, and so, some sort of mini-nuclear reactor would have to be installed. This would be not only immensely difficult and expensive but would also be extremely dangerous and overkill, as the nuclear reactor would outlive the other components of a forklift. On the other hand, Uranium has a specific energy density of around ~80,000,000 MJ/kg and an energy density of ~1,500,000,000 MJ/L, which is many orders of magnitude more than electric or combustion fuels. Perhaps with some technological improvements, this could be a viable power source for forklifts in the future.

Antimatter:

Antimatter has the highest possible energy density of ~90PJ/kg (90,000,000,000MJ/kg). This is due to how it annihilates with normal matter, releasing all of the energy within the atoms (100% efficiency). If this technology could be developed, 10 micrograms of antimatter would be enough to run a forklift for its entire lifespan. As it stands, this idea is very farfetched, as we have only created 15 nanograms of antimatter for the entire human history. Perhaps one day, this could be the perfect power source for everything.

To drive home the changes in the magnitude of the energy densities, the average fuel density, and specific fuel density are graphed logarithmically in figure 3. We can see that batteries are the least energy-dense, followed by combustion fuels and hydrogen, and both nuclear and exotic are in a league of their own. Although the differences in energy density between exotic fuels, combustion fuels, and electric sources are great, there exist other factors which make some of them better than others. The following section discusses what I think would make for a good power source for next-generation forklifts.

Energy Densities Source

Step 2: What Power Source Is the Best for Next-generation Forklifts?

The previous section hopefully gave you a good overview of various forklift power systems. This section is devoted to my argument as to which one is the best candidate for next-generation forklifts.

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As it stands, I believe that combustion engines are not suitable for the future. Combustion engines are loud, full of vibrations, produce noxious gasses, and require fuel to operate. The former three are inconvenient and make combustion engines inferior to electric ones. A source that can produce electricity is more desirable than a combustion engine, and so they are the candidates for the future. Although, they are not as significant as the need for combustion engines for fuel. As we expand to other planets, and as natural recourses within our planet dry up, we will need to be able to still operate forklifts. There is no other planet within our solar system other than Earth that both have a combustible fuel and an oxidizer for said fuel. The only way to operate combustion engines would be to bring over fuel from the other planets, which would be extremely inefficient, not to mention, expensive.

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The next generation of forklifts will be electric, and must also come with either a source of energy that will not be refueled in its lifetime (Exotic Sources) or a way to store electric energy that can be produced from the environment locally (e.g. Sun, Wind, etc.). As of now, the non-refueling sources, Antimatter and Nuclear Reactors. are not sufficiently developed to be used as sources. We do not know if it is possible much less how to create a small and powerful reactor, like the kind we would need in a forklift. These technologies may begin to exist within a few generations of forklifts, but they will not be used in the next generation of forklifts. So, we turn to methods of storing and retrieving electric power.

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Storing electric power suffers from major issues, primarily: the low energy density of electric batteries, quick degradation of electric batteries, and its long recharge time. The long recharge time is acceptable, as long as the forklift lasts throughout the workday, and can fully recharge overnight when it is not being used (overnight). As for the quick degradation of electric batteries and their low energy density, I believe that a potential solution is to use Hydrogen as a medium to store and generate electric power.

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A closed-loop hydrogen system could be formed, in which hydrogen and oxygen are reacted in a fuel cell, with the leftover hydrogen and oxygen being re-pumped back into the fuel cell, and the produced water being collected. To 'refuel' the vehicle, a current, such as the one produced by solar panels on the other planet, could be passed through the collected water, which will produce hydrogen and oxygen, which could then be separated and compressed to replenish the fuel of the vehicle.

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Unlike a chemical battery, this would not suffer from chemical degradation (if parts are resistant to hydrogen & oxygen, then only mechanical wear). No cathode or anode would degrade, nor no chemicals to break down, and if any part breaks down, it can be simply fixed or replaced. Hydrogen also has a great energy density of ~120MJ/kg & ~10MJ/L, much better than any battery or compressed gas.

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The next section discusses a potential design, and models this design in Fusion 360 to show what implementation may look like.

Step 3: Begining the Modeling

Modeling my idea in Fusion using data and calculations allows me to see how my design would fare in the real world, and to give a graphical representation to better communicate my ideas with collaborators.

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To begin, I start by sketching the general overview. I make sure that all of the most critical parts are in place. Then, I continue by modeling the body of the forklift after various reference images and modeled to a realistic size. The first image is that of my sketch, and the second is that of my completed body.

Step 4: Modeling the Tanks

My design for the forklift requires 3 tanks, a hydrogen one, an oxygen one, and a water one. The image above shows these 3 tanks.

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A typical forklift uses an 8-gallon LPG tank, which corresponds to ~30 Liters. The energy density of an LPG is 25MJ/L, and so we know that a typical forklift needs 750MJ of energy. Hydrogen has an energy density of 10MJ/L at 70Mpa, and so we need a 75L or greater tank that can withstand that pressure. This requires a wall thickness of ~5cm at an outer diameter of ~45cm. Since the height does not affect the wall thickness needed, I extended it as long as possible. My modeled tank holds around 110L.

We then need a tank of oxygen that has 1/2 the number of atoms like hydrogen, as the formation of water takes 2 hydrogen atoms and 1 oxygen atom. This is modeled in as well, with a similar pressure and wall thickness, but a smaller volume.

The water tank is designed to hold 300 Liters of water at atmospheric pressure, as that would be able to hold all the hydrogen and water if it was all reacted.

Step 5: Electrolyzer, Compressor, and Seperator

Next, the electrolyzer, compressor, and separator are modeled. The electrolyzer is simply a wire that feeds to the electrodes within the water tank, which electrolyze the water. The cathode and anode must be platinum-coated to protect them from corrosion during electrolysis. The produced gas then flows into a separator, which separates the two gasses based on their weight. The then separated gasses are compressed, and they flow into their original tank.

Step 6: Recirculator and Fuel Cell

The fuel cell is the one at the top corner of the image, and the recirculatory pumps are to the left and below it.

There was not much information on how to calculate the size of the fuel cell, so, I chose arbitrarily to go with a size that is around half the water tank. Since the gas is depressurized to 1 atmosphere before it enters the fuel cell and because the 250L would have to pass through over multiple hours, I felt like half of the water tank size would be acceptable.

The pressure system is a combination of 2 pumps, pressure sensors, and a smart controller. Any hydrogen or oxygen that is not used in the fuel cell is sucked out and sent back into the fuel cell. As well, the smart controller controls the flow of gas from the hydrogen and oxygen tank to regulate the amount of each gas and pressure in the fuel cell, to make sure it operates at atmospheric pressure.

Step 7: Conclusion

This concludes my journey in investigating forklift power systems. I believe that a Hydrogen Battery is the best way to store energy for a forklift, as it provides an energy-dense, noneroding and replaceable system, that will fare well with the future of humanity. I hope that you learned something new, and have a good day :)