Scania's launch of the OC13 gas engine marks the start of alternative fuel solutions for the new truck generation.
The OC13 is based on Scania's well-proven 13-litre engine. The engine works according to the Otto principle with spark plugs and complete combustion. It provides 410 hp and gives 2000 Nm from 1100 and up to 1400 rpm. These figures compare well with diesel engines of a similar size. With LNG, a semi-trailer truck of up to 40 t can drive 1100 km without refuelling. With twin LNG tanks on rigid trucks, a range of up to 1600 km is possible.
There is a growing interest in operating vehicles on biogas or natural gas in countries such as Italy and France as a result of increased availability, improved infrastructure and good economic viability for hauliers. The sustainability aspects are also important – even natural gas provides a CO2 reduction of approximately 15%.
Scania's gas engines are based on stoichiometric combustion, i.e. complete combustion of both fuel and oxygen. Similar to a petrol engine, the combustion is initiated by means of spark plugs. The pre-mixing of the fuel takes place upon entry into the cylinders.
"Throughout development, our aim has been to ensure the best possible driveability," explains Folke Fritzson, Senior Engineer at Scania R&D and part of the team developing Scania's gas engines. "The performance and characteristics should correspond to that of a modern diesel engine."
The new 13-litre gas engine is always available with Scania Opticruise, Scania's automated gearboxes. This means, of course, that gear changing and driving comfort are top-class for the driver, with fast, unhesitating gear selections.
Carefully thought-out tanks
The tank solutions are an important aspect of gas fuel operations. Both LNG tanks and CNG tanks can be ordered directly from Scania. LNG always provides greater range, as a significantly larger amount of fuel is available.
"In combustion, there is no difference between LNG and CNG, but there are significant differences in the operational range," says Fritzson. "With LNG, it's up to 1100 km for a typical semi-trailer on a flat road. CNG usually provides a range of up to 500 km. The latter is more than sufficient for many customers, for example in regional transports with a return to the home base and refuelling every day. The mileage that can be achieved before refuelling is required also depends on the type of driving and usage, and how hilly the route is."
In order to improve safety, Scania's engineers have turned the tank valves backwards, away from the direction of travel. This is a seemingly simple but important detail that reduces the risk of the valves becoming damaged if hit by stones or gravel.
Longer maintenance intervals
Gas engines that operate according to the Otto principle (with pre-mixing of fuel and spark plugs) have shorter service intervals than diesel engines. However, Scania has achieved a significantly longer service interval, with the lifespan of the spark plugs currently setting the limit.
"We have defined the interval at 45 000 km for both the spark-plug and oil changes with normal use," says Fritzson. "This is a clear improvement over previous generation gas engines, with 30 000 km as normal intervals. This reduces maintenance costs and increases availability."
"Everything indicates that we are heading towards a breakthrough for gas engines, including heavier trucks for long-distance transport and construction-site vehicles," says Henrik Eng, Product Director Urban, Scania Trucks. "Everyone can now benefit from good driveability and driver comfort. We also see that the rapidly growing gas infrastructure in several European countries spurs interest in using this alternative fuel."
Read the article online at: https://www.lngindustry.com/liquid-natural-gas/08112017/scanias-latest-gas-engine-designed-for-long-distance-transport/