In the 19th-century many inventors, entrepreneurs, and tinkerers, were on a mission to invent and innovate for a better internal combustion ...
In the 19th-century many inventors, entrepreneurs, and tinkerers, were on a mission to invent and innovate for a better internal combustion engine (ICE). Like so it happened with British engineer James Atkinson how had sought ways to improve on the Otto four-stroke combustion engine, which was first produced in 1876.
He patented his version of an ICE in 1882 that had variable stroke lengths with a multi-link connecting rod setup between the piston and the flywheel. Although, Atkinson’s engines weren’t commercially successful then, his thermodynamic cycle is still widely used today, mainly in ICE-electric hybrid engines.
The key advantage of his ICE was higher efficiency than that was achievable in an Otto engine, albeit with some power loss at lower engine speed. The Atkinson cycle was found ideal for hybrids because their electric motor(s) could make up for the lost low-speed output, but the higher efficiency at mid-high rpm range meant a better overall fuel efficiency and hence low running costs.
In key functioning of Atkinson cycle is that it delays the intake valve’s closing until the piston has completed 20 to 30 percent of its upward travel on the compression stroke. As a result, some of the fresh charge is driven back into the intake manifold by the rising piston so the cylinder is never completely filled (hence the low-speed power reduction).
However the engine now has less work to do in the compression stroke against the power stroke. So the payoff comes after ignition when the piston begins descending on the expansion (also called power) stroke. Consistent with Atkinson’s original thinking, the shortened intake stroke combined with a full-length expansion stroke squeezes more work out of every increment of fuel.
Exhaust cycle is same to that of an Otto cycle engine, so difference there.
In most engines, the compression ratio is set as high as the engine can stand short of detonation in pursuit of power and efficiency. Compression and expansion ratios are the same in an Otto engine. Atkinson wins on efficiency because its expansion ratio is significantly larger than its compression ratio.
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