Compressed Natural Gas Direct Injection

Joint development program “NICE” initiated by the European Community and specifically supported by DaimlerChrysler, Siemens and TU Graz.

The Technology

The CNG-di combustion system is featuring a central mounted gas injector closely located to the spark plug. The injected gas-jet is guided by a specifically designed piston bowl. The impulse of the gas-jet initialises a toroidal rotation of the mixture cloud (red arrows in Figure 1), whereby the rotation direction depends on the jet cone angle. The stability of the mixture formation carefully has to be matched with the swirl charge motion of the intake air (blue arrows in Figure 1).

The injection strategy is varied according to the respective operation condition of the engine, which may be “early” for good homogenisation as well as “late” for stratified lean operation.

The compression ratio of the CNG-di concept is chosen by 1:14 for naturally aspiration and 1:13 for charged operation. Due to the high knocking resistance of CNG, the CNG-di combustion technology preferably can be applied to charged engines. Even the fact that gaseous injection of CNG does not offer the possibility of charge cooling as it is applied with liquid fuels, this fact cannot be see as a barrier for utilising very high specific power ratings with this combustion system.

The Benefits

The Background

The Injection System

Test Results

Summary & Outlook

Acknowledgements

AVL may express the thanks to contribute in the NICE program initiated by the European Community and for the support from DaimlerChrysler, Siemens AG and TU Graz, and also to all other participants of this program for giving the opportunity to publish these intermediate results.

For further information please contact

AVL List GmbH / Product Line Gasoline Engines
Hans - List - Platz 1
A - 8020 Graz, Austria
eMail: hubert.friedl@avl.com
Phone: +43 316 787 – 664
Fax: +43 316 787 - 750