CNG and downsizing—over 30 percent lower CO2 emissions

The combination of downsizing and running on compressed natural gas (CNG) provides the potential to drastically reduce CO2 emissions. MAHLE has analyzed the potential and associated challenges using a reconfigured downsizing engine both with engine testing and in a test vehicle.

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With an optimized engine design, CO2 emissions were up to 31 percent lower.

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Stuttgart, September 2015 – With the combination of downsizing and running on compressed natural gas (CNG), MAHLE demonstrates that the ongoing development of the combustion engine continues to be worthwhile. With an optimized engine design, CO2 emissions were up to 31 percent lower. This remarkable result, however, is only possible if the components can withstand the extremely high requirements of monovalent CNG operation. As a leading engine specialist, MAHLE has the expertise required to develop the complete system.

CNG-powered vehicles from various manufacturers have been on the market for many years now. Their engines were originally designed to run on conventional fuel and therefore utilize the majority of the CO2 potential purely by substituting fuel—which can already improve emissions by up to 24 percent. Further optimization with CNG-specific development is faced with the still relatively low number of CNG vehicles produced.

MAHLE has now investigated the potential for further reducing CO2 emissions with a combination of downsizing and CNG. In a first step, the well-known MAHLE downsizing engine—a three-cylinder, single-stage turbocharged gasoline engine with direct injection and 1.2-liter displacement—was adapted for dual operation with natural gas and gasoline. The engine was then tested and applied on the engine test bench, and integrated into a test vehicle and measured. The goal of the first step was to demonstrate the potential and limits of the bivalent variant, determine potential optimization focus, and identify the associated challenges. The results form the basis for the second step, in which an optimized, monovalent design and the application of the necessary engine systems and components will be implemented

In order to ensure that the engine components can meet the extreme requirements for pressure resistance and thermal diffusity, MAHLE has planned to use the following technologies for the monovalent variant:

  • Pistons: the EVOTEC® RSC combines high stability and optimal cooling due to its cast-in ring carrier and cooling channel.
  • Ring pack: optimized for friction losses and wear, with three-piece oil control ring
  • Connecting rod: keystone connecting rod with pressed-in bushing for better dissipation of the higher surface pressure
  • Valves: sodium-cooled hollow valves on the intake and exhaust sides for increased temperature resistance, with a reinforced bottom plate
  • Piston pins: pins with DLC coating
  • Bearings: polymer-coated connecting rod bearings (sputter on bronze) and main bearings (aluminum-bimetallic)

Tests at MAHLE indicate that the required peak pressure resistance and higher temperature limits are possible by optimizing the basic engine. This also means that specific power output of 110 kW/L and nominal torque of 270 Nm (above 1,600 rpm) are possible in monovalent CNG operation with the MAHLE downsizing engine. A family van with a curb weight of 1,700 kg can thus achieve CO2 emissions of about 106 g/km, putting it nearly 31 percent below the current gasoline variant with comparable driving performance.

MAHLE is a leading international supplier to the automotive industry. With its products for combustion engines and their peripherals as well as solutions for electric vehicles, the group addresses all the crucial issues related to the powertrain and air conditioning technology—from engine systems and components to filtration to thermal management. MAHLE products are fitted in every second vehicle worldwide. MAHLE components and systems are also used off the road—in stationary applications, for mobile machinery, as well in railroad, marine, and aerospace applications.

In 2014, the group generated sales of EUR 9.94 billion with around 66,000 employees. Today, MAHLE is represented in over 30 countries with 170 production locations. At 16 major development locations in Germany, Great Britain, Luxembourg, Slovenia, the USA, Brazil, Japan, China, and India, more than 5,000 development engineers and technicians are working on innovative solutions.

Further queries:
Ruben Danisch
Corporate Communications/Public Relations
Pragstraße 26–46
70376 Stuttgart
Phone: +49 711 501-12199
Fax: +49 711 501-13700