The Dakar Future strategy embraces battery-electric and hydrogen options, with the latter to include the introduction of a common buggy platform that competitors can opt to have powered either by a fuel cell plus electric motor or by an IC engine. We understand that this 2023 machine, the details of which are still under consideration, will be a large enough to carry a considerable quantity of gaseous hydrogen compressed to 700 bar, as befits the length of Dakar stages.
Pipo Moteurs is developing this hydrogen-fuelled I4 turbo for the 2023 Dakar Rally
Liquid hydrogen would be preferable from the packaging perspective but we understand that this possibility has been rejected on safety grounds. Meanwhile, Pipo Moteurs is developing an IC engine that will use the 700 bar gaseous hydrogen supply to obtain the organiser’s power output cap of 300 kW (402 bhp).
The base engine is Pipo Moteurs’ bespoke 2.0 litre I4 turbo World Rallycross (WRX) unit, as profiled in depth in RET 107 (December/January 2018). This 85 mm bore engine has an aluminium structure, albeit with nickel silicon carbide-coated steel liners. It has four valves per cylinder at an included angle of 39º, these having steel coil return springs and opened via domed tappets by chain-driven DLC-coated camshafts.
Run by a full engine management system, the distributorless engine will be direct rather than port injected in its Dakar hydrogen-fuelled (HICE) guise. Pipo Moteurs’ general manager Fred Barozier noted that since hydrogen is low in density, port injection costs volumetric efficiency, while the presence of hydrogen in the manifold brings a certain amount of risk. Moreover, the lack of lubricity compared with gasoline is a potential threat to valves and valve guides that is overcome by the use of direct injection.
Since the hydrogen supply is pressurised, no fuel pump is required, and the fuel rail will be fed via pressure regulators to obtain injection pressures in the 30-50 bar region. Bespoke solenoid-operated injectors will be used, larger than for the direct injection version of the WRX engine and one per cylinder.
A new cylinder head has been developed that allows these to be either vertically (top) or horizontally (side) mounted in the light of development evaluation. Indeed, Barozier noted that there will be a second iteration of the HICE once the lessons of the development engine have been learned.
In general, the current HICE head follows the pattern of the WRX engine, aside from smaller valves to make more room for the injectors. In fact, the valve sizes will follow those of the first-generation WRX engine whereas the current version exploits larger diameter valves. Of course, there isn’t a push to develop output given the Dakar power cap.
The hydrogen combustion process is relatively fast and low temperature. Hydrogen burns six times faster than gasoline and can be run extremely lean. The stoichiometric air-to-fuel ratio for the complete combustion of hydrogen in air is about 34:1 by mass. However, approaching stoichiometric, combustion becomes difficult to control. Barozier anticipates running around lambda 2.3, “to keep combustion under control”.
Barozier also noted that hydrogen exhaust gas is cooler than petrol exhaust, and that there is a need for high flow from the turbo compressor, despite there being relatively low energy on the turbine side. In view of this challenge a new Garrett turbocharger is under development such that the plenum pressure can be maintained as high as 4.5 bar absolute.
In general, hydrogen fuel is less potent than petrol, but the HICE mandatory output cap is in any case only two-thirds of WRX power. Barozier added that the power cap imposed by the organiser puts the emphasis of development firmly on enhancing efficiency.
The WRX compression ratio of 10.5:1 has been maintained. However, while combustion is low temperature relative to petrol, the fact that hydrogen burns quickly creates high peak pressures, imposing considerable loading on the cranktrain. “The effective compression is almost double [that of the WRX engine]. Although the output is only 300 kW we require the strength of the WRX engine, especially in the pistons and con rods,” Barozier remarked, confirming that the WRX components can well withstand this HICE operation.
The direct injection of hydrogen has led to a new piston crown design and a revision of the intake porting. The cam profiles are also bespoke. Instrumentation specialist Horiba is currently assisting in development of the engine through instrumentation to check its efficiency, the presence of hydrogen in the lubricant, emissions and so on. At the time of writing, ahead of Dakar 2022, it was too early to be sure which teams will embrace this fascinating HICE solution in January 2023.