Lonewarrior
New Member
Has it ever come across anyone's mind that it seems a bit weird that with a compression ratio of 13.5:1 engine but only 87 octane is required?
Octane 87?
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I won't claim to understand the Atkinson Cycle on which the Clarity's engine is based, but I'm sure that's what makes this high-compression/low-octane combination work. Mazda's Skyactiv-G system with an even higher 14:1 compression ratio also works with 87 octane fuel.
Robert_Alabama
Well-Known Member
https://hondanews.com/en-US/honda-a...378955-honda-two-motor-hybrid-electric-system
"In all versions of the system powering 2014-2022 Accord and 2020-2022 CR-V, a 2.0-liter DOHC i-VTEC® engine (LFA1) is used, while the smaller Honda Insight is equipped with a 1.5-liter DOHC i-VTEC® engine (LEB-MMD). Each gasoline engine uses a high compression ratio (13.0:1 to 13.5:1 for the 2.0-liter, 13.5:1 for the 1.5-liter), but thanks to advanced combustion chamber design, precise combustion control and anti-knocking technologies, each is able to operate using regular unleaded fuel."
Honda probably does something like is described for the Prius in this document:
https://www.motor.com/magazine-summary/driveability-corner-february-2011/
"This Atkinson cycle yields some interesting engine management control. This Prius 1.5L engine has a 13:1 compression ratio. If the intake valve remains open for half of the compression stroke, the effective compression ratio is 6.5:1. The Prius Atkinson cycle engine offers electronic control over compression ratio and effectively mimics a variable displacement engine. Also, from an efficiency standpoint, the Prius Atkinson cycle mimics a short compression stroke and long power stroke. Visualize it like this: A 6.5:1 compression stroke and a 13:1 power stroke. This extracts maximum power from the power stroke. The “average” Prius engine’s operating compression ratio is 8:1."
"In all versions of the system powering 2014-2022 Accord and 2020-2022 CR-V, a 2.0-liter DOHC i-VTEC® engine (LFA1) is used, while the smaller Honda Insight is equipped with a 1.5-liter DOHC i-VTEC® engine (LEB-MMD). Each gasoline engine uses a high compression ratio (13.0:1 to 13.5:1 for the 2.0-liter, 13.5:1 for the 1.5-liter), but thanks to advanced combustion chamber design, precise combustion control and anti-knocking technologies, each is able to operate using regular unleaded fuel."
Honda probably does something like is described for the Prius in this document:
https://www.motor.com/magazine-summary/driveability-corner-february-2011/
"This Atkinson cycle yields some interesting engine management control. This Prius 1.5L engine has a 13:1 compression ratio. If the intake valve remains open for half of the compression stroke, the effective compression ratio is 6.5:1. The Prius Atkinson cycle engine offers electronic control over compression ratio and effectively mimics a variable displacement engine. Also, from an efficiency standpoint, the Prius Atkinson cycle mimics a short compression stroke and long power stroke. Visualize it like this: A 6.5:1 compression stroke and a 13:1 power stroke. This extracts maximum power from the power stroke. The “average” Prius engine’s operating compression ratio is 8:1."