The
environmental demands on trucks are becoming steadily tougher and
already this autumn, emissions will be toughened still further in
Europe. Pressure for the development of environmentally optimised
technology is increasing, but the answer need not lie solely with
electric and hybrid solutions. Tomorrow’s most energy-efficient
engines are already more than a hundred years old. All the
indicators are that the diesel engine still has a lot to
give.
Rudolf Diesel could scarcely have been aware of the historic
importance of the patent application he submitted to Kaiserlichen
Patentamt in Berlin in February 1892. His application bore the
modest title "Neue, rationelle Wärmekraftmaschine" (New Efficient
Thermal Engine), yet the invention he presented was anything but
modest. Behind patent number 67207 lay a combustion engine that was
far more efficient than any of the steam- or gas-powered engines
that were common at the end of the 19th century.
Today the diesel engine is one of the most exciting and promising
technologies in the hunt for new engine solutions for an
increasingly eco-aware and resource-efficient world. The reason for
the diesel engine's success lies in Rudolf Diesel's original idea:
to create an engine with the maximum "thermodynamic efficiency
rating" - something that is achieved when as much as possible of
the fuel's energy is used to propel the vehicle instead of
literally going up in smoke. What is special about the diesel
engine is that it compresses both air and fuel under immensely high
pressure. When the fuel in the cylinder ignites owing to the heat
generated by the high degree of compression, this generates the
power that sets the piston in motion.
The first functioning diesel engine came in 1897 and it boasted an
efficiency rating of 26 percent, way beyond the mere 12 percent
efficiency of the contemporary steam engine. Today's modern trucks
are powered by diesel engines with an efficiency rating of about 46
percent. A significant development, to say the
least.
So what exactly has happened over these past decades?
"The diesel engine's development can be divided into three stages.
The first step was the rapid development of the fuel injection
system which took place in the early 1900s. Around 1940 system
pressure had increased from 300 bar to more than 700 bar, which
meant combustion was both quicker and more efficient," says
Maximilian Prager, expert in combustion engines at the Technical
University of Munich.
The second step was taken with the development of new air
compressors, a component that soon became a problem since
compressors at the end of the 1800s were both large and heavy. With
the mechanical supercharger and later the turbine-propelled
turbocharger, which Volvo Trucks was the first company to introduce
in trucks with the unveiling of the TD100 in 1956, air pressure
could be doubled from 2 bar to more than 4 bar. This further
improved the engine's efficiency.
"The most recent major step came with the development of the
electronic common rail injection system at the start of the 1990s.
This builds up a kind of pressure reserve that can be used to
inject fuel several times per operating cycle. This both raises the
power output of the engine and reduces emissions," explains
Maximilian Prager.
All these improvements meant that the diesel engine could
strengthen its lead over other engine types. A conventional petrol
engine, for instance, today offers a maximum efficiency rating of
about 40 percent, which in terms of fuel consumption gives far
lower overall efficiency.
"In terms of the number of litres per kilometre, the diesel engine
is about 20 percent more efficient than a petrol engine. For one
thing, you can get ten percent more energy out of a litre of diesel
than from a litre of petrol, and for another, the diesel engine
operates about ten percent more efficiently than the petrol engine
does," continues Maximilian Prager.
The diesel engine's high energy efficiency puts it in the lead even
when it comes to emissions. However, it was long regarded as
"dirty" since it produced large quantities of visible smoke
consisting of unburned carbon. Nonetheless, with the development of
modern particle filters these emissions have been cut to a minimum.
And with the latest SCR (Selective Catalytic Reduction) technology,
emissions of nitrogen oxides too have been considerably
reduced.
Clear-cut examples of how the diesel engine has been improved over
the years can be found for instance in the Volvo Trucks' engines,
which in the space of just 20 years have become 100 times cleaner
in terms of emissions of climate-impacting air pollutants. In
parallel, power output has increased by 100 percent in 35 years.
Not least the flagship Volvo FH16 with its 700 hp engine - the
world's strongest truck - has succeeded in combining performance
with environmental consideration in an entirely new way. The truck
builds further on SCR technology but with the help of a range of
new technical solutions, including a new oil thermostat, improved
exhaust brake, new piston design and a new type of engine oil, it
has succeeded in maintaining fuel consumption despite
record-breaking power levels.
"By further developing the exhaust brake, which helps reduce the
burden on the wheel brakes through electronic control, we have been
able to delete a number of moving parts. This results in better
reliability, reduced weight and improved control," says Henrik Ask,
engineer and project manager for the new D16 engine at Volvo
Trucks.
Through optimised combustion and improved exhaust filtration, the
other engines in the latest Volvo Trucks driveline range have also
been made both more fuel-efficient and cleaner than ever. For a
truck with the best-selling 13-litre engine and automatic Volvo
I-Shift transmission, for instance, fuel consumption and carbon
dioxide emissions are cut by up to three percent in one single
move.
The new generation of engines meets the EU's new exhaust filtration
standards, Euro 5, which will come into force in October this year.
Among other things, these standards reduce nitrogen oxide emissions
by about 40 percent compared with the previous Euro 4 standard.
But if all this is already history, what can we say about the
diesel engine's future?
"The next 10 to 15 years will be tough for engine developers as
regards the increasingly stringent exhaust emission requirements.
However, I believe that for example Volvo Trucks' strategy -
focusing on optimising both combustion in the engine and
after-treatment of the exhaust gases - is the right way ahead.
Focusing solely on combustion with high efficiency at low emissions
will be too expensive," says Maximilian Prager.
At the same time, there is immense potential in the new diesel
technologies that are currently being developed, he feels. Biofuels
can help further cut emissions. And hybrid diesels with
single-point technology, where the diesel engine is optimised
solely for long-distance operation, for instance, may promote both
higher efficiency and lower production costs in the
future.
"There is immense potential in the diesel engine, primarily for
large engines which have to work both hard and long. The diesel
engine's high efficiency rating makes it quite simply indispensable
in the development of tomorrow's engines," says Maximilian
Prager.
Engine facts - D16G
Type designation D16G700 EU5SCR-M
Max power at 1550-1800 r/min 700 hp (515 kW)
Max revs 2000 r/min
Max torque at 1000-1550 r/min 3150 Nm
Displacement 16.1 dm3
Compression ratio 17.3:1
Exhaust brake effect at 2200 r/min 230 kW
Engine braking effect (VEB+) at 2200 rpm* 425 kW
Dry weight (base engine) approx 1325 kg
*VEB+ is available as an option.