Making sense of responsible motoring
At this very moment, Diesel owners are being demonised, when only a few years ago they were being encouraged. Petrol cars are now on the up, electric cars are being promoted like never before. Some are even considering LPG again, where as this fuel was once all but forgotten.

So I have recently found myself thinking, what actually is the cleanest fuel? What are the real facts?

Which is the cleanest fuel?
24th October 2018
Carbon Dioxide (CO2)

Carbon Monoxide (CO)

Oxides of Nitrogen (NOx)
Particulate Matter (PM)
Hydro Carbons (HC)

Effects on the greater environment, and global warming

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In reality this is actually a two sided question, because pollution can effect us in two different ways. First there is our immediate environment; the air around us that we breath in. Then there is also the greater world, the environment, the ozone layer, global warming.

So we shall deal with this question in two parts. Then, after carefully analysing everything we shall have a final conclusion. So without further delay… lets push on with our first part, the effects on the greater environment.

For the purposes of this article we shall be exploring Petrol, Diesel, LPG converted Petrol, Electric/Petrol Hybrid, and Plug-in Electric cars. There are other variations available; for example Diesel Hybrids, or LPG Hybrids, but we shall focus on these most popular types.

Some of you may have read the last article What is air pollution?, from September. For those that have not, we discussed that there are five main products of pollution, which are as follows:

Because we are first looking at what effects the environment as a whole; global warming, we are only initially interested in which fuel produces the most CO2. The other pollutants only have a very minor (if any) effect on the wider environment, and are more important to the air that we breath. This makes the first part of our investigation nice and simple.

With Diesel and Petrol cars, CO2 levels are published everywhere, and are the main factor in the taxation to the owner and driver of a given car. Ten years ago, it was widely published that Diesel cars produce far lower CO2 levels than Petrol cars, thanks to their greater fuel efficiency. Therefore they became increasingly popular, and have only recently been demonised by Politicians and the media. This is actually largely unfair, because the benefits to the environment are completely genuine. It is regrettable that some vehicle manufacturers felt the need to cheat on emissions tests, which has resulted in some of the recent bad publicity.

So because they are easy to compare, lets first compare Petrol, and Diesel vehicles. We'll pick a small family car, a medium family car, a large family car, and an executive car. This will give us a cross section. I have picked cars made around 2008, so we have a picture from 10 years ago.

From the table above, you can see straight away why Diesel was popularised as a clean fuel over the last decade. But I suppose it is fair we check on how things have changed with new cars, so here is a new list of brand new models:
Table of 10 year old vehicles
Table of brand new (2018) vehicles
If we compare 2008 with 2018, although we can see that there has been a large improvement in CO2 levels all round, the most noticeable differences are with Petrol engines. However this has come at the expense of performance, and most of the above Petrol models are vastly outperformed by their Diesel counterparts, this is in stark contrast to cars 10 years ago.

So the above has established the Diesel car as the initial winner when it comes to CO2 levels and preventing global warming. This may come as quite a shock to those who have been reading the newspapers recently. However this does ask the question about other fuels, such as Hybrid, Electric and LPG cars. So we shall add these into the mix too.

Firstly, an LPG conversion can be carried out on pretty much any Petrol car. It results in lower running costs, thanks to the lower taxation on LPG, but what we are interested in is the CO2. Converting a car to run on LPG will reduce its CO2 output by around 11%, however just as we must consider the production of Electricity when calculating the CO2 levels of an electric car, we must also do the same with LPG. The process of refining LPG results in slightly less CO2 production than that of Petrol (around 4%) so the overall reduction in CO2 levels when running a car on LPG is 15%. We can apply this to the Petrol cars in our tables:

Table of 10 year old vehicles
Table of brand new (2018) vehicles
So looking at these tables, and comparing them with the figures for Diesel and Petrol, it is apparent that LPG cars are not the cleanest solution, in fact the Diesel solution is only equalled by an LPG version of the latest Ford Focus, the rest of the time a Diesel car is better.

This may be a surprise to some readers. LPG vehicle owners enjoy reduced running costs, because the taxation on the fuel is far lower. It is the idea that LPG cars are much cleaner for the environment, so the reduced taxation encourages their usage. It seems that the Diesel owner is being treated very unfairly!