When comparing diesel combustion to petrol combustion, keep in mind that diesels ignite under a Constant Pressure process (or can be examined using this model), not Constant Volume process which petrol combustion occurs.
With the same compression ratio, a petrol engine will be more efficient than a diesel.
Also, with the ease of ignition between octanes, its all relative to the activation energy required. A crude analogy,
Its easier to compress a sponge ball with your hands (compress 91 using the compression stroke)
than it is to compress a styrofoam ball with your hands (compress 98 using compression stroke)
however with the aid of hammer adding energy (spark plug igniting, adding enough energy to reach the activation energy) you can ignite both, with the same relative ease.
With the same compression ratio, a petrol engine will be more efficient than a diesel.
Also, with the ease of ignition between octanes, its all relative to the activation energy required. A crude analogy,
Its easier to compress a sponge ball with your hands (compress 91 using the compression stroke)
than it is to compress a styrofoam ball with your hands (compress 98 using compression stroke)
however with the aid of hammer adding energy (spark plug igniting, adding enough energy to reach the activation energy) you can ignite both, with the same relative ease.
