Pump it up (when you need it)

Two-stroke VCR developments will raise and lower compression ratios during operation. Picture: WinGD

Engine efficiency has been limited by the need to avoid potentially damaging peak pressures. But supposing you could alter those pressures on the hoof, adjusting for load while the engine was operating?

It’s the idea behind Variable Compression Ratio (VCR) systems, which aim to change the reach of the piston rod. “If you have low loads, you want to burn a smaller amount of fuel. So moving the piston’s top position upward in the cylinder raises the compression ratio and makes combustion more efficient,” explains Dominik Schneiter of WinGD. “A higher load requires a larger amount of fuel, so then you lower the piston’s top position, helping avoid thermal overload.”

Admittedly, “the idea is an old one”, says Schneiter, but there’s a renewed surge of interest, driven by the increasing focus on efficiency and pollution control. Firstly, it could yield better engine performance across a broader operating range. Marine main engines are typically run at intermediate (50% to 75%) loads while hardly ever getting above 90% of their maximum power rating.

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