When the CH4-air mixture approaches the lean fuel state, the flame speed accordingly decreases, the flame cone rising and retreating downstream to the area with lower flow speed.

从化学计量向贫燃料状态靠近时，预混火焰强度减弱，火焰传播速度 减小，锥形火焰面逐渐增高，退到流速较低的下游区域；

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They do predict that the sales mix will lean toward more fuel-efficient vehicles.

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Smart advertising and relentless data-crunching fuel this lean company.

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Additional tax credits for choosing hybrid, fuel cell, alternative fuel and advanced lean-burn technology vehicles have been offered since 2005.

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