Engines have been much in the news recently, as a number of deaths have been attributed to smoky old generators pressed into service during the Sharjah power cuts. This brings to the fore the ongoing debate around the world about engines, and inparticular the need for diesel engine makers to clean up their act.
For an engineer, however the diesel motor is something of a paradox – on one hand it follows the same principals as the man from whom it takes its name. On the other, ever more demanding emissions rules from legislators, and efficiency needs form users mean that the blueprints grow more technical each year.
However, engine companies have been up against their toughest challenge to date, as a new standard referred to as ‘Tier IV/Stage 3b’ comes in to force.
This standard means that the amount of unburnt hydrocarbons, more commonly known as soot, must be brought down to the sort of level that is going to make the exhaust almost cleaner going out, than the air being drawn in. Ironically, as we will see, some of Rudolf Diesel’s original design elements are being reintroduced as the drive for more pressure, more power – and literally more ‘bang for your buck’ continues.
Diesel
Modern diesel fuel will burn relatively cleanly in the right engines. The problem is that most of the diesel available in the region is far from modern.
Old refining methods mean that local juice is likely to have a much higher sulphur content as well as containing a mix of toxic heavy metals, notably palladium, but also a variety of other nasties.
Selective
‘Selective catalytic reduction’ or SCR is a very technical way of getting a catalytic converter to work effectively.
To put what is a complex process into layman’s terms, a regular catalytic converter, such as what you might find on a car, works by introducing a ‘catalyst’, usually platinum, to a chemical reaction, which renders the end product (in this case the exhaust gas) relatively harmless.
SCR differs by using a liquid ‘reducing agent’ actually a fluid which is sprayed onto the catalyst. At one time the chemical used was ammonia, to kill the nitrous oxide (NOx) by converting the output of industrial boilers into harmless diatomic nitrogen or water.
These days, a number of manufacturers have adapted this technology for use in roadgoing diesel engines, but by using an injection of a chemical based on the substance found in animal urine known as urea, the NOx is knocked down by up to 95% with no other toxic by products.
There are a variety of different systems on the market at the moment, though as using urea injection is not mandated in the Middle East, few users take advantage.
One notable exception is the RTA in Dubai, which is using the stuff across its fleet.
Elsewhere in the world, notably in Europe this technology has been wholeheartedly embraced with all on-road truck makers with the notable exception of Scania, embracing the technology.
Forced Air
One of the defining principles of Diesel’s original design was that compressed air was supplied with the fuel, enabling combustion at an atomic level so every particle is entirely burnt.
Improvements in injector technology have rendered this concept obsolete for about 100 years, but now the idea is coming back into vogue, as engine designers try to make every last drop burn completely.
Plant Derv
Contrary to popular belief, running a vehicle on so-called biofuels is not automatically any cleaner, nor in many cases will manufacturers honour the warrantees of users who have tried it.
Properly refined though, there is no reason why it can’t be done. Indeed, Rudolf Diesel himself tried refining peanut oil when no refined fuel was available, with excellent results. Environmental politics aside, the main problems with it come down to gumming and glazing.
‘Gumming’ refers to sticky deposits that build up in the fuel line, which can block injectors, particularly in modern ultra-high pressure injection systems, while ‘glazing’ refers to the varnish-like build up that can be left by such fuels.
Rudolph Diesel – A life under pressure
Way back in 1903, the company boss of MAN trucks, one Heinrich von Buz, became interested in the plans for an invention known as the ‘rational heat engine’ being developed by inventor Rudolph Diesel.
There was a problem though – the engine simply wouldn’t run as the necessary pressure could not be achieved. Diesel wanted to compress – and thus heat – air in a cylinder with such great pressure that only a tiny amount of fuel would be needed to generate an explosion and drive the cylinder piston. But the pressure Diesel hoped to attain – over 150 atm– originally even much more – wasn’t possible, as it was based entirely on theory by the university scientist Carnot.
This didn’t deter Diesel from trying other methods to raise the pressure. Sources say he worked tirelessly, on occasion blowing things up but always coming back for more.
It took years, but as he wrote: “the desire to realise the Carnot process dominated my existence”. Eventually, he had to admit to himself that the science was junk, and the engine was never going to run. It was at this time that he set about re-writing the rule book, and developed the forebear of the engine that now bears his name.
The tale doesn’t have a happy end though – he had taken his designs to the UK, but on the ship back one night in 1913, he disappeared. Most credible historians suspect he was dispatched by German agents, as his designs were politically sensitive ahead of the First World War.
