Mercedes Putting New Natural Gas Sprinter Van Into Series Production
11 March 2008
|The Sprinter NGT|
Mercedes-Benz is putting its Sprinter 316 /516 NGT natural gas van into series production, with market launch targeted for May 2008. The company began showing prototypes of the Sprinter NGT at vehicle shows last year. (Earlier post.)
Although Daimler has offered a natural gas version of the Sprinter since 1997, this is the first time the company has built a compressed natural gas version of the Sprinter from first principles. In the past, the NGT Sprinters have used a conversion from a gasoline engine—the M 111 E 23.
The engine on the Sprinter NGT is also applied in Mercedes-Benz passenger cars. Mercedes-Benz uses a bivalent system—the basic engine, a four-cylinder unit with a displacement of 1.8 liters, will also run on gasoline, extending the range of the Sprinter up to 1,200 kilometers (746 miles).
The driver can switch between the fuels by pressing a button to the left of the ignition lock. An indicator lamp comes on when in natural-gas mode. A display in the cockpit also lets the driver know how much gas is left in the tank.
Equipped with a belt-driven supercharger with a compressor, the engine develops 115 kW (156 hp) and reaches maximum torque of 240 Nm (177 lb-ft). Both figures apply both to natural gas and gasoline mode. The predecessor Sprinter NGT had a rated output of 95 kW/129 hp, with torque of 185 Nm. The natural gas-powered Sprinter is fitted with a six-speed manual transmission as standard, and comes with the option of a driver-friendly torque converter.
|Gas storage in the new Sprinter NGT.|
The gas tanks are installed beneath the floor to save space and avoid restricting the cargo load at all. The 3.5-tonne Sprinter can accommodate up to six tanks that hold a maximum of 46 kg or a volume of 294 liters. The model with a gross vehicle weight of 5.0 tonnes uses three tanks that hold 39 kg or 246 liters.
The Sprinter NGT meets the Euro 4 emissions standard. Emissions of nitrogen oxides, hydrocarbons and carbon dioxide are reduced substantively compared with the diesel engine. Compared with the gasoline engine, the NGT delivers a CO2 emissions reduction of around 20%, plus reduced carbon monoxide and hydrocarbons. The Sprinter NGT is virtually CO2-neutral when powered by biogas.
Operating costs with natural gas in Germany are up to 30% lower compared to an equivalent diesel version.
Daimler plans a wide range of variants for the Sprinter NGT: the Sprinter 316 NGT, for instance, with a gross vehicle weight rating of 3.5 tonnes comes as a panel van, crewbus, pickup and chassis in the standard length. A long-version panel van, pickup and chassis are also available. A pickup and chassis are also available under the designation Sprinter 516 NGT with a gross vehicle weight rating of 5.0 tonnes.
Note that Germany is offering tax breaks on CNG through 2018, so fuel cost per mile is below that of a comparable diesel vehicle.
I wonder why they picked a supercharger rather than a turbo. In a vehicle like this, the engine will spend much of its life cruising at high load anyhow. Transient performance due to turbo lag is only an issue at stop lights etc., but it can be overcome.
At low loads near idling speeds, a turbo normally spins at just ~20,000 RPM, so it is ineffective and the engine operates much like a naturally aspirated one.
By reversing the flow of fresh charge through the compressor wheel in that operating region, it becomes a cold air turbine driven by the pressure differential between the ambient air at the intake and the partial vacuum generated by the receding piston. All you need to implement the flow reversal is some extra ductwork, valves and control software.
Since both wheels act as turbines, more bearing friction can be overcome and the shaft spins at high RPM (~80,000 RPM) in spite of low exhaust gas enthalpy.
As soon as the driver depresses the accelerator pedal again, air flow through the compressor wheel is switched back to normal mode. Boost pressure is now available almost immediately because the shaft is already spinning rapidly.
The hard issues are optimizing the compressor wheel geometry for both operating modes and, executing the mode transitions very rapidly to avoid stalling the engine.
Reference: Dissertation M. Mueller, "Der Radialverdichter im Kaltluftturbinenbetrieb - auf dem Weg zur drehzahlstationaeren Turboaufladung", TU Karlsruhe, Germany, Oct. 2007 (in German). Logos Verlag Berlin, ISBN 978-3-8325-1736-6
Posted by: Rafael Seidl | 11 March 2008 at 10:42 AM
rafael, doesn't the veriable geometry turbo design with vanes on the turbine side perform a similar task of increasing the speed of the wheels by reducing the inside volume of the turbine chamber? I am just a mechanic/student but I have noticed they use this design on diesels and have reduced lag to almost nothing. With CNG you would also not have the carbon and soot problems that we see inside the turbo on diesel powered vehicles.
Posted by: JW | 12 March 2008 at 06:21 AM
I believe that problem is with higher exhaust temperature of gasoline engine. It makes construction of VGT so expensive that only 911 Turbo can afford it.
I'm sure Rafael will have more on that :)
Posted by: Mirko | 12 March 2008 at 07:15 AM
@ JW -
Mirko's reply is unfortunately correct and applies to all stoichiometrically operated (i.e. virtually all spark ignition) engines, regardless of the fuel used.
However, engineering consultancy Ricardo recently proposed a concept they call "EGR-boost". In essence, it relies on recirculating 20-30% of the exhaust gas at low pressure, i.e. removing it downstream of the turbine wheel and three-way catalyst, cooling it and injecting it upstream of the compressor wheel.
Since exhaust gas is inert and has higher caloric values (three-atom molecules) than air (two-atom molecules), this permits not only a reduction in throttling in part load but also cooler combustion and hence, lower engine-out exhaust gas temperatures at high load. The latter sharply reduce or even eliminate the need to enrich the air-fuel mixture to protect downstream components and, permit the use of a VGT turbo made from affordable materials.
The hard part is keeping water vapor from condensing in the EGR ducts and cooler, because that would enable the formation of corrosive sulfuric and phosphoric acids. Condensation droplets would also pose a threat to the compressor vanes.
Posted by: Rafael Seidl | 13 March 2008 at 06:36 AM
If you run this on biomethane you have a zero CO2 vehicle...can't beat that...next to no NOX and particulates, zero CO2, large range, not a conversion...fantastic idea....
Posted by: John Baldwin | 13 March 2008 at 03:10 PM
Posted by: JW | 13 March 2008 at 09:31 PM
Does anyone know if this vehicle will be available in the USA?
Posted by: Sam Swearngin | 17 March 2008 at 10:06 AM
Does anyone know if this vehicle will be available in Brazil?
Posted by: Ana | 02 April 2008 at 12:49 PM
is there any van(vw,toyota,benz....)with gas engine?
Posted by: majid | 14 April 2008 at 12:02 AM
How can we find out how much the 516 NGT panel van is going to cost?
Posted by: Ash | 01 May 2008 at 01:31 AM
Does anyone know if this vehicle will be available in Croatia ? How much will cost ? I have new MB Sprinter 518 minibus 20 seats I will sell it and buy this one. The prices of fuel went in Croatia high.
Posted by: Florio | 14 May 2008 at 04:17 AM
As the Sprinter in diesel is imported to North America and requires crash testing etc. What potential is there to bring the CNG version to this market in light of the growing momentum of natural gas in our markets. I work for a large gas utility in Toronto and there is a new Provincial Government program being launched that incentivizes 30% of the incremental cost of the CNG option for Class 3- 8 trucks Minimum over 10,000lb GVW.
Manager NGV Sales
NGV Business Development
(905) 238-8027 Ext.227
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