So how is the natural gas revolution going?
Let's talk about the heavy-duty fuels capable of providing the backbone of road freight transport
If electricity is bound to replace gasoline in cars, natural gas has every right to threaten the status of diesel as a fuel for vans, trucks, buses and all things heavy-duty. Formerly natural gas was heralded as the clean fuel of the future, but did that future already arrive or after the hype settled down it became a failure? Let's investigate.
Not all natural gases are equal
The goal of this article is to give an overview about the three alternative fuel types considered ideal for heavy road traffic: CNG, LNG and hydrogen. The three-letter abbreviations may seem alien at first, but don't worry, everything will be discussed in depth.
Properties of fuel types most commonly used in commercial vehicles.
So what is natural gas exactly? The thing originates from the same hydrocarbon deposits as crude oil, but forms under higher pressure. It is very energy-dense, so makes ideal fuel for power stations, homes or even vehicles. It's clean burning, producing minimal amount of carbon residues and since still many oil company consider it a by-product it's dirt cheap. It can also be produced from decomposing biological matter in which case it is referred to as biogas. Autogas (LPG - liquified petroleum gas, also known as propane-butane) shall not be confused with various natural gas derivatives, it's a by-product of gasoline manufacturing.
Differentiating between odourless and colourless gases can prove difficult, but pre-conceptions may help.
Some may be surprised that electricity is not compared as an alternative, but the common judgement of the industry is that there is an upper weight-limit for battery electric vehicles around 4-5 tonnes. Designs above that limit would waste more energy carrying their own batteries than they could utilize for towing useful weight, so while in theory a 40 tonne battery-electric truck with 1000 km range is possible, it would be very inefficient. As a side note: such vehicles (mainly transit buses) do exist, but historically using trolley networks proved far superior and some cities even experimented with trolley-trucks.
CNG: Compressed Natural Gas (nat. gas @ 200 bar)
The most common form of natural gas is what you find flowing from the gas pipe in your home: about 85% methane (CH4), a bit of ethane (C2H6) and a minimal amount of longer hydrocarbon chains. CNG is simply that gas cleared of water and squeezed to fit into a reasonably sized tank. No refinery or petrol station required, just put a strong compressor on a residential gas line and you can make your own CNG fuel.
The image is not missing anything, CNG filling is really that simple. Image courtesy of Motor Jikov.
Okay - before you'd do that there are same safety precautions, for fast filling a couple of buffer tanks are also required and unfortunately most country will treat you as a criminal for fuel tax evasion, but CNG is an easy to understand matter. It can be used in very straightforward engine setups, forget DPF, AdBlue, EGR and special lubricants - it's back to basics, the exhaust gas doesn't require any special after-treatment even for relatively strict standards such as EURO6. In practice it's mostly used in spark-ignited (Otto-cycle) engines, though in theory it can also work in diesel conversions.
Public natural gas filling station heat map of Europe as of 2015. Image courtesy of GRTgaz.
So if it's really that great why isn't it everywhere? Problem is that after taxes CNG is only a tiny bit cheaper than diesel and states don't really appreciate the clean burning if it still yields CO2 in the end. Also, despite being compressed, natural gas tanks still require relatively big space to store enough fuel for a daily routine, limiting range to around 350 km in practice, though CNG containers are usually complemented with a gasoline tank for bi-fuel operations, meaning you won't need to worry about having to search for a service station that sells your favourite fuel. Also, CNG vehicles are no longer expensive - as mentioned before they don't require the development and fitting of high-tech emission control technologies. Currently a CNG powered Iveco Daily van retails for around 27.00 €, which is in the same price range as it's diesel-powered equivalent. It really varies by markets and use-case whether a CNG vehicle's total cost of ownership is lower than that of a diesel. The generic conclusion is that for fleet operators with high mileage and moderate load (such as postal service or parcel delivery) switching to CNG is worht considering, especially if they can afford to set up their own filling station, because natural gas compressing isn't really a complex task.
CNG tanks take up a lot of space, even if smart engineering can disguise this problem.
There are also passenger cars manufactured with CNG tanks, Fiat and VW brands (Audi, Volkswagen, Seat, Škoda) all offer natural gas powered vehicles and they enjoy some niche popularity in markets like Italy, Germany, Austria, Switzerland and Ukraine (Ukraine is a black sheep as the country has no oil refinery, they are more reliant on natural gas as an energy since they broke relations with Russia). Cars like the VW eco up! or the Fiat Panda Natural Power can be had for about half the price of a similarly sized EV.
LNG: Liquified Natural Gas (nat. gas @ -162 °C)
LNG is CNG's chillier brother - natural gas liquifies at low temperatures, which solves the main issues mentioned before: space and range. When cooled down to liquid state it only takes up about 1/3 of the compressed gaseous matter and only 1/600 of the volume it would take up under atmospheric circumstances, so it is very compact. Yet, it also introduces a new problem: how to cool down something to that low temperature? A giant freezer called LNG train is just made for that purpose, as LNG is also the form of natural gas used for transcontinental gas trading. It turns out that -162 °C required to keep the gas liquid is not that exotic at all - in fact as you read these lines dozens of giant LNG carrier ships are sailing the world's oceans with incredible amount of cold natural gas onboard. They burn away some of the LNG in the process to keep the shipment cold, but it works and thanks to the scale of the economy cooling is relatively cheap, primarily close to sea ports with LNG terminals. But can it be cheap enough for road freight?
Koinè is just one of the numerous trucking and logistics companies already operating LNG haulers in Europe.
The strict measures required to control the liquid state makes LNG a fuel for only the heaviest and most frequently used vehicle categories that have to cover great distances on the highways with massive capacity, so don't expect it to be available for your next Peugeot hatchback. However, almost every major truck manufacturer now offers LNG variants of their flagship models and it turns out there are buyers too. The most frequent solution for injecting it to the cylinder is mixing it with diesel for ideal combustion, but spark-ignited variants also exist.
Another side effect of the low temperatures is the boil-off phenomenon. After the truck has been filled up, the surrounding air starts warming up the fuel, no matter how well insulated the tank is. The liquid natural gas has to be used as quickly as possible, ideally within a few days or part of the valuable fuel turning into gas has to be vented out into the environment through a safety valve. Once the fuel starts boiling, the tank can no longer hold it's pressure and the expanding liquid would rip it open from the inside. As a result, LNG should only be used for frequent journeys where the truck is constantly moving and shouldn't be filled up if it's going out of service. It requires special circumstances to be profitable over a diesel variant, but the number of freight companies already operating LNG trucks is promising.
Hydrogen (reformed from nat. gas)
Let's bust a common misconception: hydrogen is not produced from water at industrial scale. The process requires more energy than the end product provides, so unless there is some excess power source (such as unused solar power) electrolysis is a wasteful process for educational purposes. Retail hydrogen is reformed from natural gas - in a nutshell: they take the methane (CH4), the main component of natural gas and remove that one sole carbon atom from the molecule with the use of oxygen. That means there is no CO2 emitted while you drive around your vehicle, but it isn't really a green fuel either, as the methane reformer produces CO2 as you'd do through burning it in natural gas form.
Legislators don't care about what happens at the producer though, as currently they are focused on the exhaust pipe to measure emissions and this situation is unlikely to change, meaning hydrogen's future is looking bright. But it doesn't really have a present. There are many startup companies like Nikola Motor developing hydrogen fuel cell drivetrains (burning hydrogen in a combustion engine is generally not a good idea) and the Toyota Mirai is also a well-known example of hydrogen cars, but spotting hydrogen-powered trucks in the traffic is impossible at the moment.
Despite the fancy fuel cell buzzwords the Toyota Mirai is indirectly a natural gas consumer.
Hydrogen mobility is at a very early experimental state - even more so than LNG. The explosive nature of hydrogen makes it challenging to adapt it for everyday uses - even gasoline and natural gas shouldn't be toyed around with -, and the necessary level of safety can make it somewhat expensive for small scale uses. So while it can combine all the benefits of CNG and LNG with eliminating the disadvantages - it's compact, non-polluting and energy-dense - it's not really an affordable thing yet, but it is forecasted to sooner or later show up in heavy duty trucks as the power potential is huge.
So do we have a winner? Not really, all types of natural gas are made for different uses - CNG is already very widespread in many European countries and it's easy to use: if you are thinking about ditching your diesel for something less polluting and not too expensive that's the way to go. LNG is for huge trucking fleets constantly on the move, while hydrogen is really just a promise of the future. While diesel and gasoline are constantly threatened by regulations and price wars, the natural gas economy seems to have a nicer outlook with gas reserves being more abundant and emissions far lower. Engine technology and the complexity of delivery can vary, but natural gas as a road fuel is no longer science-fiction, it's a reality. Now we just need to adapt to it.