A report entitled Enhanced Emissions Support and Fuel Efficiency for HD Methane Engines, prepared by AVL MTC Motortestcenter AB for the International Energy Agency – Advanced Motor Fuels, may be of interest to decision-makers considering the introduction of methane fuel HD engines. This literature survey was conducted in order to define the state-of-the-art for methane-fuelled engines to be used in heavy-duty vehicles. The use of methane can increase energy security, mitigate CO2 emissions, and potentially reduce toxic exhaust emissions.
The project compiled data on methane as fuel for different HD engine technologies and looks at the associated costs for aftertreatment of exhaust emissions. Additionally, weak points of the Diesel Dual-Fuel (DDF) system are identified and also a proposal for a road map for recommended further work is presented.
AVL lists the following main conclusions:
• The drivers for using methane are different in different countries but main reasons are mitigation of CO2 emissions, mitigation of toxic emission and access to low cost fuels.
• The general trend for OEM might be towards stoichiometric engines with TWC (three-way catalyst). One alternative technology pathway is lean burn engines either SI or Diesel Dual-Fuel (DDF) with sophisticated (and possibly also expensive) aftertreatment of the exhaust.
• The main advantage of using DDF is a potential for better fuel efficiency than the traditional SI-engine, due to the Diesel-like process.
• Further development of methane fuelled engines has to be carried out in order to meet future emission regulations (Euro VI), especially the part of regulations specifying limit values and durability.
• Exhaust aftertreatment systems for dedicated methane fuelled HD vehicles have to be further developed to minimize the degradation, normally caused by “poor” design of the converted Diesel engine.
• Conversion from Diesel to DDF is very attractive for vehicles operating in long haul operation but DDF concepts have to be developed further to be able to meet stringent emission and durability requirements.
• European emission regulations must be further adopted in order to cope with engines using two fuels simultaneously at various mixing rates. Cooperation with the informal group for Gas Fuelled Vehicles (GFV) within the GRPE (UNECE) is recommended. Items to discuss are test procedure, methods for calculations of emissions, test fuel to be used and limit values for DDF-concepts.
• Development of procedures for verification of emission performance of methane fuelled HD vehicles in real life operation is essential for assuring proper function of the complete exhaust control system during the life time of the vehicle.
• Since advanced emission control and engine management system is required to meet latest emission requirements, the gas application should be designed as a complete system and not only as a stand alone unit. We identify difficulties to meet these requirements without a close cooperation between OEM and suppliers of gas systems.
• A sustainable principle for setting the price for methane must be introduced giving stakeholders a long term schedule for further development of methane fuelled vehicles. The main objective should focus on methane fuelled vehicles as a cost efficient alternative as well as a vehicle with low level of exhaust emissions during the useful life.
• A common position about methods for calculation of CO2 equivalent GHG reduction from different methane based fuels should be adopted to enable the most cost efficient methods for future production of methane fuel and engine technologies.
The full report, available to the public, can be downloaded here.
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