Gulf Construction Online - Diesel is back to the future

Environment Protection & Waste Disposal

Volvo tailors engine performance to the requirements of each machine.

Diesel is back to the future

Diesel is not the dinosaur of the engine world – it has a brilliantly bright future, says engine and construction equipment manufacturer Volvo CE while dispelling some myths about the working of modern diesel engines.

01 December 2004

Apart from a few exceptions down the decades, construction equipment have had diesel engines.

But isn’t diesel old-fashioned, dirty, smoky, noise and on the verge of being replaced by super-modern hydrogen fuel cells?
Well, no. Modern diesel engines are none of the above; and fuel cell technology is only in its infancy.
The fact is that recent developments in diesel engine technology have revolutionised almost every aspect of the performance of diesel engines – fuel consumption, emissions, longevity, reliability and power. Far from waiting for retirement, diesel engines have a brilliantly bright future.

The basics
Like petroleum-powered engines, diesel engines are ‘four stroke’ combustion engines. But unlike petrol, which is a ‘spark ignition’, diesel uses a ‘compression ignition’, meaning the increasing cylinder pressure and corresponding heat that is created ignite the fuel. This in turn means that diesels don’t need the spark plugs, coils or plug leads that petrol engines use. In fact, a basic diesel engine doesn’t need any electricity at all to run. The engine compression ratio is also very high; air is compressed down to about 1/18th of its original size. This is much higher than in petrol engines and implies that diesel engines have to be stronger to cope with the higher pressure.
For a given engine displacement (that is 8 litre, 10 litre, etc.), diesel’s compression ignition system allows more air to be used in the combustion process compared with a similarly-sized petrol engine. This greater amount of air allows more fuel to be used and results in more power generated for a given engine displacement, compared to a petrol engine. Recent fuel injection system advances now allow electronically-controlled direct fuel injection. These fuel systems replace the traditional mechanical system and result in more precise control of the fuel injection process. Advantages of these new systems include increased power, lower noise, improved fuel consumption and improved engine response. Also, because these systems ensure that the fuel is burnt very efficiently, the engines emit fewer emissions, thereby reducing their environmental impact.

Power & torque
Whenever you talk about engines you invariable hear the terms power and torque. But not many people know more than high numbers are generally better than low ones on machines’ specification sheets.
In construction terms, engine torque determines how much gravel can be lifted by a wheel loader for a given engine speed. Power determines how fast the gravel can be lifted. Both are important parameters but what is most important is how well both are matched for the equipment’s operating speed. This is why it is better to have equipment companies who develop and match their own engines for their own applications.

More power
Naturally aspirated (non-turbocharged) engines use only the quantity of air that is drawn into the engine from the piston movement. The use of a turbocharger (or supercharger) allows more air to be forced into the engine. Again, the high compression ratio of diesel’s compression ignition system allows for a higher level of turbocharging than is possible with spark ignition engines. This higher quantity of air allows more fuel to be used – resulting in more power.
The difference between turbocharging and supercharging is how the device is driven. Both take air from after the air filter and increase its pressure before introducing it to the engine. A turbocharger uses engine exhaust gases to drive its internal compressor and a supercharger uses an engine-driven belt or gear drive to rotate its internal compressor. But because turbos use ‘waste’ energy, they are more efficient than superchargers, which need to be driven directly by the engine.
To have even more power from a turbocharger, the air is cooled before introducing it into the engine. As air is compressed, its temperature rises and it becomes less dense. By cooling air, its density increases, which results in more oxygen becoming available for combustion. This optimisation of combustion air and fuel has resulted in diesel engines having higher fuel consumption efficiency.

Extending durability
Not only are diesel engines powerful and efficient, due to their inherent simplicity and strength, they are also very durable. But that’s not to say that their longevity can’t be improved upon. There have been developments in both cooling and lubricants, resulting in a reduction in corrosion, erosion and signs of wear.
Water may be a ubiquitous resource but on its own it can cause problems within an engine’s cooling system. Such defects can include rust, scale, acidity (leading to corrosion) and pitted cylinder liners. This last problem can be caused by cavitation, where tiny bubbles in the water implode when the cylinder fires – and these tiny explosions wear away at the lining of the engine.
Scale reduces the engine coolant flow, resulting in higher engine operating temperatures and corrosion may weaken engine components. However, keeping cooling systems clean, along with regularly replenishing with conditioners (which form a protective lining) can reduce build-up of scale and engine corrosion. Care needs to be taken with conditioners though, as it is possible to have too high a concentration.
The same is true with engine oils, which reduce friction, cool the engine and remove contaminants from the engine. Oil needs to be regularly flushed through and replaced with the correct oil grade. Not all oil is of the same type or quality, so it’s important to use oils that have been developed for the particular engine’s requirements. Using the recommended oil and regularly changing oil and filters are key factors for a long engine life.
Another key factor is the air filter, which prevents engine contamination. This is particularly important in a construction environment, which can have extreme levels of particulates in the air. Care must be given in the exchange of air filters in a construction environment to prevent system contamination. Not changing the filter regularly – or not using the recommended replacement – can lead to a reduction of the incoming air, which in turn can result in high fuel consumption.

A new era
Diesel engines are undergoing rapid and sustained change – often driven by new exhaust emissions legislation, which requires a drastic reduction of engine emissions of particulates, nitrous oxides (NOx) and carbon monoxide (CO).
Recent engine design innovations include improved turbocharger performance, flexible high-pressure fuel injection and engine control systems. Engine manufacturers are currently trying to find the best way to meet the stringent emissions regulations while at the same time continuing efforts to improve performance and efficiency.
Volvo’s new solution – V-ACT (Volvo Advanced Combustion Technology) – has been introduced to meet the requirements of the forthcoming Tier 3 (US) and Step 3 (EU) off highway emissions legislation. V-ACT combines reliable technology with a proven base engine.
Volvo is fortunate in that it is among a small number of manufacturers that make both engines and construction equipment. This means engine performance is tailored to the requirements of each piece of Volvo equipment, rather than having to adapt the equipment around the performance characteristics of other suppliers’ engines.
Engines are not just matched to the drive train, but also to the hydraulics; providing the response characteristics operators prefer for each equipment type. This produces engines that deliver optimised power and torque when and where needed, as well as smooth throttle response, low fuel consumption, low emissions and (of increasing importance) low noise.
Far from being a relic of the past, the diesel engine is now truly coming of age – and is set to cause a few surprises. New combustion technology, low emissions and fuel consumption coupled with high productivity, responsiveness and reliability mean that diesel has become the most efficient of current engine technologies.