A prototype engine that can adjust its compression ratio on the fly aims to make heavy trucks and off-road vehicles run cleanly on renewable fuels like bioethanol. The problem is that many commercial vehicles—trucks, construction equipment, generators—are hard to run on batteries. They need long ranges, quick refuelling, and high power. Renewable fuels exist, but they burn differently from petrol or diesel. Bioethanol, for example, produces extra hydrocarbon emissions during cold starts because fuel condenses on cold engine surfaces, causing misfiring. This project tackles that mismatch. The engine, built on Libertine’s ‘intelliGEN’ opposed free-piston platform, can raise its compression ratio for the first few seconds of operation, compensating for heat loss and burning the fuel more completely. If it works at scale, it could let heavy vehicles run on low-carbon fuels without requiring a full battery-electric switchover. Many commercial vehicles sold in 2030 will still be on the road in 2050, so making them compatible with net-zero fuels now is a practical step toward decarbonising transport that cannot simply plug in.
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The proposed 12 month project will develop and demonstrate a variable compression ratio range extender engine optimised for heavy duty vehicles with renewable fuels, building on findings from the successful feasibility study demonstration completed in Phase 1\. In Phase 1, discussions with potential future customers identified the need for a performance validation prototype engine as the next key milestone on the path to commercialisation of Libertine's 'intelliGEN' Opposed Free Piston development platform. In Phase 2 a performance validation engine will integrate Libertine's 'intelliGEN' platform with subcontractor MAHLE Powertrain's MJI passive pre-chamber internal combustion systems, and will implement multiple enhancements for thermal management, durability and electrical power conversion efficiency in order to achieve extended test operating durations and validate performance against customer requirement specifications. Libertine's 'intelliGEN' Opposed Free Piston development engine systems provide the means for OEMs to develop new products making full use of renewable low carbon fuels. These products will be essential for the decarbonisation of 'hard to electrify' transport applications including heavy duty commercial vehicles, heavy duty off-highway vehicles, for a proportion of light duty commercial vehicle and passenger automotive segments where vehicle use and recharging constraints are a barrier to electrification, and for a larger range of distributed power generation applications. The variable compression ratio and non-sinusoidal piston motion capabilities of Free Piston Engines have the potential to enable cleaner and more efficient use of renewable biofuels and synthetic low carbon 'e-fuels' owing to the combustion characteristics of these new fuels. In particular, renewable alcohol fuels such as bioethanol have a high heat of vaporisation and whilst generally clean burning, with fewer harmful emission than gasoline, can produce increased hydrocarbon emissions at cold start due to un-vaporised fuel on cold chamber surfaces ('wall wetting') resulting in persistent misfiring. Phase 1 demonstrated that this negative impact can be reduced using an elevated compression ratio during the first few seconds of cold-start operation to compensate for heat loss from the air/fuel mixture. Many of the new commercial vehicles sold in 2030 will still be on the roads in the UK and worldwide by 2050\. To meet the objectives for net-zero transport in 2050, it is therefore essential that the majority of commercial vehicles sold in 2030 are compatible with net zero carbon fuels for those journeys, and use cases, where recharging is not yet economic, practical or convenient.
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