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Auxiliary Power Units

The range of electric vehicles is often limited by the useable energy capacity of the onboard batteries. Range can be extended by carrying an onboard charging source known as an Auxiliary Power Unit (APU). Our focus was on optimising current APU technology and developing new ideas for the next generation of Range Extended Electric Vehicles (REEV).

Achievements include:

  • A roadmap of current and future auxiliary power unit technologies
  • A technical requirements specification for an APU
  • A packaging study integrating the APU into an LCVTP GTV vehicle, including studies to optimise the NVH characteristics
  • An analytical study of the benefits of REEV compared to other architectures
  • Testing and analysis to inform and validate future APU design
  • Testing and analysis to optimise APU after treatment to achieve legislated emissions levels
  • APU hardware to demonstrate a new APU utilising a state of the art volume production gasoline engine and a Ricardo designed bespoke generator in a REEV GTV vehicle


Business Impact – New Products and Processes
Working together, the project partners undertook the major task of designing, building, testing and validating a new auxiliary power unit which utilised a state of the art volume production gasoline engine. They also worked closely with the drive motors team to integrate a bespoke design APU generator.

Tata Motors European Technical Centre (TMETC) and Ricardo used simulation software to evaluate the potential efficiency benefit of using Atkinson & Miller cycle engines for APU applications; the TMETC analysis was validated by converting an existing Otto cycle engine to Atkinson cycle operation for objective measurements at MIRA. Computer simulation models were also used to investigate the benefit of a wide range of other base engine modifications for the specific APU duty cycle. The results will be used to inform the design of future APU engines.

Ricardo and MIRA worked together testing and developing the APU hardware and operating strategies, in upgraded testing facilities. Coventry University provided support on the emissions data analysis and studied the optimum requirements for after treatment in a range-extended electric vehicle application. Ricardo integrated the new APU into a current-production Jaguar Land Rover validation vehicle.

The knowledge gained will aid the specification and design of more efficient, compact, quieter and cost effective APUs for competitive low carbon range extended electric vehicles. The results from undertaking this challenging task are already being utilised in future advanced vehicle engineering programmes.


Lead partner



Supporting Expertise

Coventry University
Jaguar Land Rover
Tata Motors European Technical Centre (TMETC)