From Euro 1 through to Euro 4 the presence of particulate emissions was measured and described by mass in terms of grams emitted per kilometre during enclosed rolling road testing. The problem is that nanoparticles weigh virtually nothing.
A new method of testing and accounting was needed, and Euro 5 introduced particle counts for diesels. In Euro 6, the current standard, particle counts for direct injection petrol engines have also been included.
Removal of sulfur from fuels has been a good thing for a number of reasons. Most importantly it has allowed the use of exhaust after treatment.
However, removing PM10 sulfur and carbon particles has resulted in the proliferation of ultrafine and nanoparticles. Why? Larger PM10 particles acted like sponges and provided a surface to which smaller particles could, and did, become attached in the exhaust. So, in effect, PM10 particles removed the much more harmful compounds in exhaust emissions. Who’d have thought.
So, there are problems built into the continued use of internal combustion engines, particularly diesel engines. So, is this the end of the line for petrol and diesel power?
Recently we were in contact with engine research company, Bennett Clayton. The group is working with alcohols and gaseous alternative fuels that it suggests could open up new possibilities for the continued use of internal combustion engines, but without the associated detrimental effects of hydrocarbon fuels.
Oxygen for the combustion of hydrocarbon fuels is drawn from air. The problem is that air is only 21 percent oxygen. The rest is 78 percent nitrogen and one percent trace gases.
Nitrogen doesn’t contribute anything to the combustion process, it just absorbs heat that could be used more productively. Nitrogen doesn’t expand very much with heat (which is why it’s used in race tyres) so it doesn’t contribute to cylinder pressure. It simply takes up space in the chamber and produces NOx.
Methanol is an oxygenated fuel. In fact, by mass, methanol is about 50 percent oxygen. So, burning methanol doesn’t require as much air as other fuels. Also, because there’s oxygen actually bound up in each molecule it’s not as reliant on coming into contact with atmospheric oxygen, although the latter is still a factor.
Overall, at stoichometric a methanol fueled engine inducts 40 percent less air in its operating cycle. Reduced, but similar advantages hold for ethanol which is 36 percent oxygen.
Importantly, alcohol fuels are also a good choice for internal combustion engines because of their molecular structure. In general, highly branched fuel molecules are less inclined to create nanoparticles as are fuels with low carbon content.
Methanol, ethanol and gaseous fuels like propane, butane, methane and dimethyl ether (DME) have these qualities. Diesel fuel, on the other hand, has long relatively straight molecules that promote the formation of ultrafine and nanoparticles.
DME is an oxygenated gas extracted from wood or wood waste. It’s high cetane rating makes it suitable as a diesel replacement fuel that requires only minor engine modifications. It can use the same infrastructure as LPG and is stored similarly in the vehicle.
One problem DME does have is poor lubricity. So, it needs to have a lubricating oil added to protect pumps and other components designed for diesel.
Other diesel alternatives do require some engine modifications, but suitably formed decompression plates can take care of that. Bennett Clayton has a great deal of experience with such modifications. Diesels modified for alternative fuels could even see such engines certified for use indoors.
Strangely, saving the internal combustion engine is linked to the success of electric vehicles. EVs are not emissions free if the electricity used to recharge them is generated by burning fossil fuels.
Their success is contingent upon non-polluting sources of electricity. If such sources are developed to the point of industrial usefulness, new possibilities for making renewable hydrocarbon fuels become possible. How? There are at least a couple of companies that have developed techniques to remove carbon dioxide from the air. Carbon Engineering has a working technology to do so using only water and energy. The company also has a compatible technology called AIR TO FUELS.
To summarise the process, CO2 is captured from the air by passing it through a patented matrix, hydrogen is created by electrolysis of water with renewable electricity and the two are thermo-catalytically combined into syngas and then further reacted into hydrocarbons.
The company is focused on producing diesel and jet fuel. However, Carbon Engineering also says it could produce any hydrocarbon. The processes involved are industrially scalable. Renewable hydrocarbons - whoever thought such a thing would be possible!
Conventionally created petrol may also continue to play a part in transportation. This is because a barrel of oil is 159 litres of various hydrocarbons. It’s refined by distillation and various catalytic cracking processes to yield about 73 litres of petrol, 35 litres of diesel, 20 litres of kerosine/jet fuel and six litres of propane. The rest is 30 litres of butane, asphalt, sulfur and other things.
As is commonly known, oil is the base for other things like plastics. The thing is, plastics are made from products like naphtha that emerge from the tops of fractional distillation columns. The issue there is that other products like petrol and diesel oil that emerge from lower sections of such towers will still be made in the process. Further processing might be applied to such fractions to convert them for other uses, but petrol is an obvious choice.
Blending alcohols with petrol might be a means of soaking up some of the petrol produced during oil distillation for other purposes. E85 is an excellent fuel that consists of 85 percent ethanol and 15 percent petrol. Bennett Clayton suggests that even a 50/50 blend of ethanol and petrol would still have an excellent emissions profile.
The availability of alternative, renewable fuels could be the savior of the internal combustion engine. Current engines could be modified to take alternative fuels.
Engine manufacturers might see the success of such installations and be encouraged to modify suitable engines from new. Concerns and regulations relating to particulate emissions could also be a catalyst for change.
Now, all of this is to say nothing about autonomous vehicles. Although it’s always assumed that they’re going to be electric, there’s no rule to say that they have to be. Electric motors are great for cars and now have enough range for most general uses. Somewhat heavier vehicles, like the Rivian and Tesla pickups, also seem to be suited to battery power. We’ll know for sure when they’re released.
But in really heavy-duty applications, it’s likely that the internal combustion engine will remain the motive force of choice, at least for the foreseeable future. So, don’t pack up your spanners just yet.
Read Is there a future for the internal combustion engine (Part 1). Alternatively, view full article and accompanying imagery in the October 2019 issue of Australian Automotive (page 32).