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Keeping it clean: Here's what you should know about Turbodiesels

2017-05-08 09:51

Lance Branquinho

CLEAN WITH TURBODIESELSouth African motorists were rather late to arrive at the performance/economy party that is the modern turbodiesel engine.Image: iStock

Cape Town - South African motorists were rather late to arrive at the performance/economy party that is the modern turbodiesel engine. 

Whilst Europeans, with the benefit of handsome diesel pump price fuel subsidies, have always preferred turbodiesels over petrols for all but the most committed high-performance applications, the South African market only started accepting truck fuel in passenger cars at the turn of the millennium. 

There were two cars crucial to this Mzansi turbodiesel awakening: Golf IV Tdi and BMW’s E46 320d. With 0-100km/h acceleration times the equal of most similarly priced petrol rivals, and vastly superior range, these oil-burning Golf and 3-Series sedans convinced South Africans that turbodiesels were a very viable alternative to their petrol-powered siblings. 

READ: 75% of SA motorists say drivers don't respect one another - report 

Immense R&D resources were deployed during the first decade after 2000, with increasingly powerful injectors and Piezo ceramic charge technology extracting terrific torque outputs from turbodiesels. All the time, constant throttle fuel economy remained about 20-30% better than any equivalently petrol engine, and for South Africans and their long-distance driving habits, turbodiesels started making an awful lot of sense. 

Unfortunately, there’s been a dark secret to the promotion of turbodiesel. And no, we’re not talking emissions and the related VW issue in the US. We’re talking diesel quality. And in South Africa, it’s terrifying. 

Fuel is the one issue which can potentially convert your creditworthy turbodiesel ownership experience into one of junk-rated ruin. 

Pressure is the problem

Turbodiesel engines available for decades, but they lagged embarrassingly in performance compared to similarly sized naturally-aspirated petrol engines. The breakthrough moment for turbodiesels came with the high-pressure, common-rail, injection systems - with fuel delivery precisely controlled by piezoelectric valves.
These piezo valves, when charged with electricity, expand and contract, allowing for incredibly precise high-pressure fuel atomisation. How high are the pressures involved? Up to 3000-bar, which is ridiculous, but also the reason that comparable 2.0-litre turbodiesel engines have on average notably more torque than similarly-sized turbopetrols.

There is a tremendous risk with these high-pressure injection systems, where tolerances are minuscule and any contaminant sourcing from your fuel, is accelerated under 3000-bar of pressure, and sure to damage the tiny opening it’s forced to travel through. 

It’s the reason there have been above-average turbodiesel failure rates in the South African market. Our diesel fuel is dirtier than Europe’s. In South Africa, diesel is still primarily refined and legislated as an industrial fuel: for heavy transport and farming use. Those engines run much lower injection pressures and can withstand higher volumes of contaminants present in the fuel delivery system. 

Your modern turbodiesel car engine, cannot.

How do I protect my engine from a costly failure?

By being conscious of what you are paying for each time your turbodiesel passenger car, bakkie or SUV is running low on fuel. The pump standard is divide into two options: 500- and 50ppm. Obviously, the latter should be your choice, with its greatly reduced sulphur content. 

It’s not merely buying the lowest ppm-rated fuel which is crucial, it’s where you buy it too. Service stations which appear old, with a forecourt that is filthy, will likely have fuel bunkering infrastructure that is similarly maintained. Poorly. And it’s during the stowage and re-circulation from delivery truck to pump, and eventually into your tank, that additional environmental contaminants can be added, escalating injector failure risk.

READ: Honda NC750X – the case for fuel economy 

The choice advice is to frequent popular service stations with new infrastructure and a high-customer throughput. These outlets receive their fuel on short haul deliveries. Why is that important? Because as a fuel tanker travels, it heats up, and if it delivers after sunset, having started drive in warm daytime temperatures, the cooling affect will cause condensation – and excess water build-up in diesel, is death to injectors. 

Service stations which are modern and exhibit the discipline of good housekeeping will have lower dust risk – and South African dust is particularly damaging to diesel engines, because it contains Silica, which clogs the injection system, or can destroy it under pressure.

A fuel-stop which has a tidy forecourt, is one which will serve you quality fuel. It’s also one which is less likely to be purchasing fuel from a bulk reseller, and often it’s in this intermediate logistically supply chain where Paraffin is added to diesel, after the core product has been siphoned off, dangerously reducing the lubricity properties of the tanked supply. 

Sasol does produce some phenomenally clean diesel for South African passenger car users on the Reef. It’s rated at 10ppm, but fuel of that quality is the exception, as the transport and bulk stowage of diesel is often afflicted by ill-disciplined housekeeping. 

The principle you should apply? Always fill-up when you see a smart service station. Don’t roll into a dust-swept rural one, with analogue pump gauges – and expect them to sell you fairy-fuel diesel which won’t damage your high-pressure engine. 

Read more on:    engen  |  lance branquinho  |  engines  |  fuel  |  fuel focus

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