BioCNG Retrofit : An innovative approach through mature technology


For CRMT, the retrofit approach is the energetic transformation of a new or an already existing diesel vehicle, to make it run only on natural biomethane, by making technical choices adapted to the targeted use case, in order to improve its environmental quality and its operational performances. The bioCNG retrofit methodology, developed by CRMT over the last 20 years has been applied and was presented at the European Mix.E trade fair by the engineering company on a school coach (ECOl’car solution) and an agricultural tractor (RES4LIVE project). Both vehicles were installed on the forecourt of the Cité Internationale, in Lyon during the exhibition.

“ECOl’car, Direction bioGNV”: conversion of diesel school coaches to bioCNG.

Context: Born from a partnership between the CRMT and the transport company Berthelet, ECOl’car is the first diesel school coach converted to BioCNG. The solution reflects the desire of transport players to accelerate the energy transition, by enabling vehicles in France to respect the air quality and to be part of the circular economy, with a local renewable energy at a competitive cost. To be developed, the ECOl’car solution was financially supported by ADEME via the AURATRANS 2021 programme and TotalEnergies. The project was approved by the CARA competitiveness cluster and supported by GRDF.

Use case: In France, a school coach drives an average of 20,000 km per year. It is checked every six months and is therefore in very good functional condition after several years of use. It does not need a long range of autonomy (300 km target) and makes little or no use of the luggage compartments.

CRMT’s retrofit approach: The vehicle was retrofitted by the replacement of its Euro V diesel engine by the equivalent brand-new CNG one (Euro VI standard). CRMT integrated the new CNG components including a new after-treatment system and adapted the diesel vehicle’s functions for CNG operation. The CNG tanks are installed in part of the luggage compartments, as these last ones are rarely used in school coaches.


ECOl’car converted coach
© Rhône ( – Converted tractor from diesel to bioCNG

RES4LIVE project: Conversion of a diesel farm tractor to bioCNG.Context: RES4LIVE (Renewable Energy Sources for LIVEstock) is a project funded by the European Union through the Horizon 2020 innovation programme, whose partners’ mission is to develop, adapt and test innovative and promising solutions for fossil fuel-free agriculture. The retrofit of the agricultural tractor presented by CRMT, provides a solution to reduce the environmental impact of a market segment for which there is not yet an alternative to diesel: small and medium-sized agricultural tractors. The retrofit work also promotes energy independence for farmers who already produce their own biogas in methanisation units, by allowing them to consume their own resources (valorization as a fuel for vehicles). Starting in summer 2022, the tractor retrofitted by CRMT will be tested and monitored at the Innovation Farm (InnvationsHof) of the Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB) located at the experimental farm LVAT (Lehr- und Versuchsanstalt für Tierzucht und Tierhaltung e.V.) near Potsdam, Germany.
Use case: The farm tractor is used on the farm, moving equipment in the morning and again in the afternoon (4 hours autonomy target), next to a biogas plant equipped with a biogas scrubber and a bioCNG compressor.
CRMT’s retrofit approach: In this project, the transformation of the vehicle involves the modification of the diesel engine base, to make it run on bioCNG. The main steps of this transformation are the following:

– Modification of the engine to adapt it to gas combustion: adaptation of the cylinder head, modification of the pistons and reduction of the compression ratio, implantation of the spark plug.
– Integration of CRMT’s gas engine control system: engine computer which controls the gas components (regulation of the air/gas mixture, injectors, ignition, various sensors).
– Adaptation of the engine control strategies to the tractor’s use on the farm (power and torque requirements).
– Addition of an after-treatment system to comply with the latest pollutant emission standards for non-road vehicles.
– Testing and validation of the CNG engine under NRMM cycle (Non-Road Mobile Machinery) at CRMT’s test benches.