The methane diesel engine differs from today’s diesel engine in that gas is injected together with air into the inlet manifold via two extra injectors per cylinder, just above the valve opening. The small amount of diesel is injected exactly as normal, compressed and then ignited, after which the air and gas mixture also ignites. Methane and diesel thus do not meet until they enter the cylinder.
“One important new development,” says Mats Franzén, Manager Engine Strategy at Volvo Trucks, “is that the system’s own ECU* is coordinated with the engine’s main ECU. We have developed the software in-house so we have the entire process under full control.”
No difference for the driver
The aim is to run on 25 percent diesel and 75 percent gas. The greatest efficiency is achieved if the methane gas is cooled to 160 degrees below zero Celsius. At this temperature, the gas becomes a liquid, its volume shrinks and it is therefore possible to carry twice as much fuel within the same tank volume.
“The driver of a truck with a methane diesel engine will notice no difference whatsoever as regards either power or driving properties compared with a conventional diesel engine,” says Mats Franzén.
Benefitting from diesel power
With Volvo Trucks’ methane diesel engine it is possible to reap the benefits of the diesel engine’s renowned efficiency, which is about 30-35 percent higher than that of today’s gas-powered vehicles which need spark plugs to ignite the fuel in the conventional Otto cycle.
“Irrespective of which fuel is used to power the two engine types, the diesel engine always offers superior energy efficiency. It is for that very reason that we see diesel engines in all heavy vehicles,” explains Mats Franzén.
One natural objection to methane is that diesel, which comes from crude oil, is a fossil fuel and it is initially being replaced with yet another fossil fuel, namely natural gas. Volvo Trucks’ Environmental Affairs Director, Lars Mårtensson, responds as follows:
“Our most important driving force behind the introduction of methane diesel technology is the energy efficiency of the diesel engine – irrespective of the fuel it uses. It is its efficiency that makes it so attractive. Natural gas is only being used as an interim solution until the infrastructure for large-scale production of biogas is up and running.
“When we can run on biogas with 25 percent biodiesel mixed in as the “combustion agent”, carbon dioxide emissions will be 80 percent lower than when running on diesel alone,” continues Lars Mårtensson.
Plenty of European filling stations
Europe has a well-established infrastructure primarily for compressed gas (CNG/CBG), while the infrastructure for liquefied gas, LNG/LBG (see the fact box), is in its early stages. In Britain there are plenty of filling stations, while in Sweden for instance there are none at all. Soon, however, filling stations will be built in Sweden’s three largest cities, partly as a result of the direction Volvo Trucks has taken.
In 2010 Volvo Trucks will carry out field tests involving methane diesel engines in Sweden and Britain. There is considerable interest, not least from the public sector which already applies tough environmental demands to purchase agreements and serves as a driver of development in this area.
“We enjoy good cooperation with dedicated customers in several countries, and our field tests aim to fine-tune the technology ahead of our broader product launch,” says Lars Mårtensson.
In this transition phase, before the fuel station infrastructure is fully established, these vehicles have the benefit of being able to continue driving on diesel alone if their gas supply runs out.
* The ECU is an Electronic Control Unit that regulates the fuel injection, ignition settings and other parameters of an internal combustion engine.
