I'm very familiar with the analysis of turbo-engines. But here's the problem with your thinking: When fuel is burned, allowing for inefficient combustion, the inefficiency is usually related to full combustion of the carbon. The hydrogen likes to be fully combusted. So, if you are using less fuel, you can't possibly be generating more water, at least for the same thrust level.
There is a simpler reason. Modern aircraft are now flying commonplace at higher altitudes. Where the air has less water vapor, true, but the relative humidity is mostly saturated. So water vapor exhausting into this air cannot remain as vapor and will condense (or crystalize), making a contrail without fail.
I grew up in the town of Bellingham in Washington state. When I was a small child, I would sit out in the back lawn on a sunny and cloudless day, and watch multi-engine jet aircraft fly far overhead, leaving behind white marks across the sky like chalk. What I was watching were test flights of B-52 bombers being built at the Boeing works in Seattle. B-52s fly at 50,000 feet. Flying at much lower altitudes (early jetliners) would only occasionally produce contrails (there was more moisture in the air, but the relative humidity was low).
I'm very familiar with the analysis of turbo-engines. But here's the problem with your thinking: When fuel is burned, allowing for inefficient combustion, the inefficiency is usually related to full combustion of the carbon. The hydrogen likes to be fully combusted. So, if you are using less fuel, you can't possibly be generating more water, at least for the same thrust level.
There is a simpler reason. Modern aircraft are now flying commonplace at higher altitudes. Where the air has less water vapor, true, but the relative humidity is mostly saturated. So water vapor exhausting into this air cannot remain as vapor and will condense (or crystalize), making a contrail without fail.
I grew up in the town of Bellingham in Washington state. When I was a small child, I would sit out in the back lawn on a sunny and cloudless day, and watch multi-engine jet aircraft fly far overhead, leaving behind white marks across the sky like chalk. What I was watching were test flights of B-52 bombers being built at the Boeing works in Seattle. B-52s fly at 50,000 feet. Flying at much lower altitudes (early jetliners) would only occasionally produce contrails (there was more moisture in the air, but the relative humidity was low).