The New Horse Petrol Engine That Can Run Underwater

Injecting water into a combustion engine isn't as daft as it sounds: it's useful in very high-performance turbocharged units, for example, to suppress detonation and allow higher boost pressure and more advanced ignition timing to gain more power.

Immersing an entire engine in water, though? That's something else altogether.

In early September, Horse Powertrain announced the waterproof B20 engine, which is capable of operating at a depth of up to 1.1 metres and is suitable for hybrids. It can also maintain continuous output under extreme high-load, off-road environments, including climbing 100% gradients. The 2.0-litre inline four makes 189-280bhp and 221-280lb ft, depending on conditions.

Large amounts of water entering an engine can destroy it instantly. Liquids like petrol and water are incompressible, so a fine mist vaporising as it enters the engine is fine but a significant quantity entering the cylinder on the compression stroke causes hydraulic lock, preventing the piston completing its compression stroke and causing severe damage. Although deep wading isn't new, with serious off-roaders using snorkels to let their engines breathe, submersion is still a challenge, as electrics and other parts need to be considered too.

The B20 meets one of the highest levels of the Ingress Protection standard, IPX8.

It's configured for efficiency, running on the Miller cycle, with 48% of the fuel it burns being converted into mechanical energy. High-pressure-injection, high-tumble intake ports promote ideal air-fuel mixing and contribute to efficient combustion.

The pistons are designed to maximise the 'squish' effect. 'Squish' describes a flat area near the edge of the piston crown mirroring a surface on the ceiling of the combustion chamber to leave only a tiny gap when the piston reaches the top of its stroke. As it does so, the fuel and air mixture is literally squished and squirted back into the centre of the combustion chamber, increasing turbulence and improving combustion.

The B20 also features a rigid, gantry-type aluminium cylinder block with integrated exhaust manifold and a simplified balancer-shaft system to improve its refinement. A variable-displacement oil pump avoids the need to consume any more energy in pumping lubricating oil than absolutely necessary, reducing fuel consumption.

IPX8 certification is achieved by the fully sealed structure and dedicated engine-to-transmission sealing. Electrical components and sensors are also IPX8-rated. The latter detect when the engine is submerged, then the control system makes changes such as limiting power or altering throttle response.