Vehicles running on natural gas are also becoming increasingly attractive in the commercial vehicle sector. This is due to the high availability of the primary energy source, its suitability for the SI combustion process, and the favorable H/C ratio with regard to CO2 emissions. For years, FEV has been working on the development of gas engines for commercial vehicles and industrial applications, covering the entire spectrum of the development process for various emission scenarios. In doing so, particular attention has been given to validating the reliability of the engines. FEV has established processes and internally developed tools for this purpose.
Complex Development Process
The development process gives rise to many challenges – especially with regard to the derivation of a natural gas variant of a basic diesel engine, which is common in the commercial vehicle sector. The use of gas as a fuel requires modifications of the engine hardware to achieve the desired gas flow, ignition, and exhaust aftertreatment. Secondly, the unit must be adapted to the modified combustion process.
The partially new engine configuration is designed and tested with regard to mechanical reliability. Adjustments are made to the engine management system for control of the gas combustion process; modifications are also made regarding safety functions, component protection, and changing boundary conditions such as gas quality, climate conditions, etc.
The most important parameters to ensure the reliability of a natural gas engine variant can be illustrated in the case of a turbo-charged natural gas engine with a stoichiometric combustion process. The derivative was adapted from an existing diesel engine and has an external, cooled Exhaust Gas Recirculation (EGR) and a three-way catalyst. Such configurations have increasingly been used for commercial vehicles since the introduction of the EURO VI emission standard and therefore represent the current state-of-the art.
The aim of the concept design is to minimize the thermal and mechanical loads. Due to the modified combustion process, these may be higher in certain operational areas than in the base engine. At the same time, high combustion efficiency levels are desired. The externally cooled EGR is used to reduce the knocking tendency and, in parallel, lower the combustion and exhaust temperatures. An adaptive knock control and various engine protection functions, including exhaust temperature limitation, misfire detection, and more are used for safeguarding.
Despite all of these minimization measures, the increased thermal stress in gas engines cannot be fully compensated. Furthermore, natural gas as a fuel causes other wear-critical effects that have to be counteracted by an adjustment of the components. To protect the engine in continuous operation, additional testing steps are necessary which FEV includes in the development process.
Opportunities and Risks
From a technical point of view, this means there are no obstacles to the widespread introduction of natural gas engines, despite the complex development process. Thanks to targeted development, the engines meet all statutory regulations and limits. Depending on the country-specific fuel prices, the operating costs of a natural gas engine can be significantly reduced compared to a similar diesel version. However, the insufficiency of the current natural gas infrastructure remains an obstacle.
>> DESPITE ALL MEASURES THE INCREASED THERMAL STRESS ON GAS ENGINES CANNOT BE FULLY COMPENSATED