So what is nitrogen? Nitrogen is a colorless, odorless gas that comprises nearly 80 % of the atmosphere. It is not very reactive, but is certainly not inert. It does form nitrogen compounds which play a big role in all living organisms and are essential to plant and animal life.
Plants require nitrogen as a basic building block in their growth and normally obtain nitrogen from nitrates in the soil. A few plants such as beans, known as legumes, fix their own nitrogen direct from the atmosphere.
So nitrogen and nitrogen compounds are good and friendly? No actually not. A nasty member of the family is nitrogen di oxide (NO2 ) , which is a brown oily gas that is very unfriendly. One lungful of NO2 will send you off to the Promised Land after a little bit of agony. . It was a favorite gassing weapon in the trenches of the 1st world war. Not fun.
So where does your Landy come in ? Unfortunately IC (internal combustion ) engines and diesels in particular produce small quantities of nitrogen oxides . Oxides ? The evil NO2 and the funny NO (nitric oxide). NO is known as laughing gas and is also used by Hein in his Disco as a Cruiser Loser – truly a useful gas ! But the environmentalists are not happy about the NO2 component. Even in moderate concentrations it can be a lung irritant , it is a known carcinogen , it promotes the formation of smog and with water vapor it produces nitric acid , a real “meneer “ of an acid. Anybody with any laboratory experience treats NO2 and HNO3 (nitric acid) with great respect.. So what can we do about the NO2 ? The automotive answer is seen to be the installation of EGR (Exhaust Gas Recirculation ) systems. And environmental legislation around NOx (NO2 and NO) emissions is being tightened.
What does the EGR do to reduce NOx ? The EGR injects a little bit of the burnt exhaust gases back into the inlet manifold. Typically exhaust gases consist of about 80 % N2 , and 20 % CO2 (carbon dioxide) , The idea is to get some CO2 back into the combustion chamber . So then we have a gas mixture entering the combustion chambers consisting of NO2 , O2 and CO2 . CO2 will not react further with the diesel fuel , but it does slow the combustion rate down . It also has a higher specific heat than the other gases so it suppresses the temperature of combustion . This drop in combustion temperature is what is needed to suppress formation of NO2 .
So the EGR is a brilliant solution to pollution problems ? Actually not at all , for a variety of reasons . Firstly it is of variable effectiveness due to design limitations. Control systems are designed to cut EGR at idle speeds and at high engine loads because at low speeds recirculation causes lumpy idling and at high speed exhaust gases cannot be injected into high pressure boosted manifolds. So it only works part time.
Secondly , EGR systems are notorious for fouling up and messing with an engine’s efficiency . If you run a TD5 – my advice is rip out the EGR already – otherwise it will punish you one day. And on TDV6’s and Pumas there are also kits available .
So what about the morality of messing with an environmental system? Well if it misbehaves , the engine will then pump out far worse pollutants than ever, in particular black smoke and CO (poisonous carbon monoxide).. Land Rover must have come to the same conclusions when they discontinued EGR systems on the later TD5’s . Secondly , I believe , that unless one lives in one of the big pollution centers of the world (e.g. California ) , the production of small quantitities of NO2 is not a bad thing. Certainly nature itself produces its own NO2 and it plays a very important part in our ecology . Every time there is a lightning strike , NO2 is produced and is washed to earth by rain. This dilute solution of NO2 is a source of nitrate for plants that do not have nitrogen fixing capability. So the NO2 that my Disco produces is actually a nutrient source for the crops that keep us fed. And with intensive farming , lighting strike nitrate is no longer sufficient, and farmers have to pour on expensive nitrate ferilizers. .Perhaps the farmers in the Montague and other areas owe the club a thank you for allowing them to cut back on their nitrate fertilizers. Certainly I remember my Tdi pumping copious amounts of NO2 into the air , while driving the Ratel !
And there is another reason that an EGR is not ideal for my Disco. Exhaust gases contain plenty CO2 ( a source of carbonic acid) , traces of SO2 (source of sulphuric acid) , traces of NO2 ( a source of nitric acid ) and solid carbon particles. I am more than happy not to introduce these items back into the combustion chambers .
So what else can we say about nitrogen and our Landys ? What about nitrogen charging of our big tough mud tyres ? That is another story that I will address another day.
Part 2
The tyres on your Landy are inflated with normal air , which is 78 % Oxygen ,21 % Nitrogen and 1 % other gases. Actually not true : we tend to forget water vapor which normally varies between 1 and 4 % . So in fact the air in your Landys tyres is approximately 75 % Nitrogen , 20 % Oxygen 4 % water vapor and 1 % other gases . It is important to realize that water vapor behaves like a gas , until it is cold and condenses , then it acts like a liquid of much lower volume. So imagine what happens when you jump out of your tent on a mountain near Montague , at 8 am in the morning and de air tyres ahead of the days drive. The water in the tyre will be condensed and lying in a little pool inside the tyre . You bring the pressure down to 1 bar , set off on the drive and an hour later the pressure has increased to 1.4 bar. Part of this pressure increase is simply the gases expanding with temperature , and part of it is due to the water evaporating inside the tyre and becoming a gas , which adds a significant contribution to the pressure increase.
Similarly you do a snow trail up the Matroosberg , park the car for an hour in the snow , the tyres cool down , the water vapor condenses , and when you drive down you find that the tyre pressures have fallen to dangerous levels . Happened to me….
So what to do about it ? Fit tyre pressure monitors . Not a bad idea , but they do not address the problem of the pressure variations. You still have to adapt to the big changes in pressure.
Use dry air to inflate the tyres ? Certainly would help , but it is not a simple matter to dry air , particularly if you use a portable compressor. (note that water traps in industrial compressors remove condensed water , but they do not remove water vapor)
Use nitrogen to inflate your tyres. The production process of nitrogen , by its nature, produces a water free product. So fill your tyres with nitrogen and you will get a dry gas that has greater pressure / temperature stability than ordinary atmospheric air has . Nitrogen also diffuses through rubber slower than does oxygen , so over a period of time a nitrogen filled tyre should hold its pressure a bit better than ordinary air . There are other advantages claimed by nitrogen suppliers – which I believe are a bit over the top.
So am I recommending that we should all rush out and pump with nitrogen ? Actually no , I think the hassle /reward ratio is unfavorable . Unless you drive a F1 car , or an airliner . I think our efforts are better channeled along more ordinary directions.
Such as pressure measurement :
After battling a bit in sand and realizing that I had to bring my tyre pressures a lot lower than I had been doing , I got around to looking carefully at the accuracy of pressure gauges. I had three pressure gauges , all with beautifully graduated and legible circular scales . They all gave different pressure readings , which is not acceptable when you are operating at pressures below one bar. So I threw them all out and popped in to Midas. I have long had the suspicion that a simple pencil type gauge offers the best accuracy and reliability . I picked up three cheap gauges , 2 of the pencil type and one a cheap electronic gauge with liquid crystal readout. The pencil types cost all of R20. Guess what – they all read precisely the same over all pressure ranges. And they are precisely correct , ( have calibrated against other systems . Why the electronic gauge ? Useful for reading in the dark . And easier to interpret the scale – so I use it to lend to other drivers who might have a problem.
I must also report that on a recent club outing at the dunes I used one of my gauges to check a few other Landys (no names , no pack drills) . Three of those I checked had differences of 0.2 bar or more. Including some expensive imported ARB systems. Now setting your pressures at 1 bar and actually getting 1.2 bar can spoil your day. So I do recommend getting two cheap pencil type gauges , and keeping them as a standard to check the expensive gauge that you might prefer using.
