Which Alternative Fuel is Cleanest?
Which alternative fuel is cleanest in terms of carbon emissions, including the energy spent on manufacturing the fuel and the engines that use this type of fuel?
Also, which one is most practical? I don’t know it air cars will be able to carry out our economy.
Electric/EV’s?
Ethanol?
Natural Gas (LNG or CNG)?
Biodiesel?
Methanol?
Compressed Air?
"Cleanest" is a relative term. Does this mean that the operator does not have to touch or think about the fuel? Does this mean that some pollutants are considered like hydrocarbon emissions but not radioactivity (coal and nuclear)? Does this mean that you are only thinking of the fuel itself and not the means to produce/recover/refine it and the original sources? Does this mean you are not considering the efficiency of the means to use this particular fuel? Does this mean that you are not considering cost or expense? Or does it mean all of these things.
There are problems with each fuel/means of production/ usage chain/cost. There are ways to maximize the advantages. Some of these things might be considered "clean" but are also greenhouse gasses and that is another problem.
Without considering any of the production means electricity would have to be the cleanest source of power because it is not exactly a "fuel" in the same sense as the others. An "EV" could be an electric train that has no batteries but gets it’s power transmitted to it by a third rail or overhead wires. But it is also not a fuel. The electrical motor is around 95% eefficient and can be made to require virtually no maintenance. The only by-product would be a small amount of heat.
When produced with "clean sources of energy like hydro or solar photovoltaic cells electricity can also seem very clean. It is only when you begin to consider that some electricity (a little less than 50% is produced with coal (or nuclear energy) or the pollution associated with manufacturing equipment that it becomes more polluting. Other sources of power would also have these considerations.
Compressed Air is far less efficient than pure electricity alone but might be considered a storage medium for electricity. As a system it is known as CAES (Compressed Air Energy Storage.) There are two types of engines being considered. One is a piston engine and the other is a rotary engine. Torque is high but efficiency is low with heat or cooling a significant by product.
The production of natural gas can be extremely polluting to the environment (water supplies) and if burned with some lack of oxygen it can produce deadly carbon monoxide. Mostly it is considered a "cleaner" fuel. As a gas it is too bulky to use in a vehicle. Compressing it to a liquid adds an element of inefficiency. It is non renewable and a significant source of electrical power generation.
The main advantage of ethanol is that it is mostly produced from renewable crops. Corn ethanol produces 1.3 units of energy for every 1 put in while the ratio for sugar ethanol is 16 to 1. Using farmland to produce fuel instead of crops might be an issues as is the amount of water required (9/10 of our water supply.)
Methanol (aka wood alcohol) is available but methane (a gas produced from biomass breakdown) is a significant greenhouse gas. It is primarily used to make bio-diesel.
Bio diesel is only slightly less polluting than regular diesel when including the production cycle. It’s main advantage is that it comes from renewable resources.
One you don’t mention is hydrogen which can be very clean but presents issues with leakage and a low energy content. Because it does not occur naturally it is essentially a form of energy storage like compressed air. As such, its cleanliness is dependent upon the cleanliness of the original sources and the amount of extra equipment required. Burning it can produce pollutants but more modern approaches suggest using this fuel in a fuel cell for an electric car. The economies are not yet available.
Synthetic fuel is said to be carbon negative in its production. But that does not stop it from producing pollutants including the release of carbon dioxide when it is burned.
A gallon of gasoline (about 6 pounds) produces about 20 pounds of carbon dioxide when it is burned (because most of the weight is the oxygen in the atmosphere that it has combined with.) There are also a few more pollutants included in its by products. All fuels when used in a heat engine are going to be subject to the laws of thermodynamics which limits any potential efficiency of the engine.
All fuels not completely burned are going to have by products. The only possible exceptions here are electricity, and its two storage mediums of compressed air and hydrogen.
biodiesel is probably the cleanest but it depends upon how it is produced. If it is produced by clearing rainforest in Brazil and planting palm oil, then turned into ethanol and transported around the world, it actually is doing more damage for the environment as it creates more CO2 than it saves.
if you produce it however from waste materials like straw or household vegetable waste then
A) it is not competing with animals for habitat and
B) it is not contributing to increased food prices too which resulted from farmers switching from growing vegetables to growing crops like canola for biodiesel.
Biodiesel from waste sources are commonly called second generation biofuels and by far the way forward in my opinion. They use waste and convert them to ethanol and then biodiesel.
we are a few years off seeing this as common practice, but I believe it is a real sustainable solution. Some operations are already up and running and using waste from tips/waste recycling centres.
hope that helps
Electric/EV’s? comes from coal
Ethanol? Comes at the expense of food
Natural Gas (LNG or CNG)?
Biodiesel? Its diesel which makes soot, comes from food
Methanol? comes from natural gas with a loss, so you use 40% more naturals gas in the long run over just using natural gas
Compressed Air? Comes from coal at low efficency as compared to a electric car, it uses 50% more coal.
Electric if the elcetricity is produced by alternative energy (hydro, solar, wind, ect.)
None of the above. It’s hydrogen. Japan has a car that runs on the hydrogen from the water. It’s already in production. The exhaust is water vapor.
Compressed air comes close but unless the power comes from hydro electric, you still need some dirty fuel exhaust to make it.