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sorry buddy, been busy with report writing and some chemical process energy balance.
There is a paper by the US Army tank command describing how they recover the water back after the injection. It has many similarities with the concept that I have, you can view it for free at
linkinghub.elsevier.com/retrieve/pii/S0082078475803985
Basically, unless we want to carry lots of water, it is necessary to condense the water in the exhaust gas, filter it and reuse the water again. So basically, I am looking for water to fuel ratio of about 4-7:1 . if there is an external supply of heat from solar or geothermal, we can bump it up to even 10:1
As stated in the paper by the us army, you need to lower the exhaust temperature to as low as 40 C to recover the water.
Yup i agree with you that compressing gas isnt 100% wasteful. However, I am coming from an angle where I am questioning on whether it is necessary to compress lots of nitrogen which does not belong in the cylinder at all? when the diesel engine run lean, there will be plenty of gas that will be compressed for nothing.
in addition, diesel engine often overcompress the charge at high load resulting the peak temperature to go above 2000K where NOx becomes a big problem.
What I am proposing is to use plenty of recycled exhaust gas to raise the cylinder temperature. Next, variable valve timing will be used to set the effective compression ratio. Let's say if we target auto ignition temperature of 1000K, we can be sure that optimum compression work is used regardless of speed and load
My calculation was based on compression work required for conventional diesel if compared to oxygen engine with exhaust gas trapping and variable exhaust valve timing. Even when all the power requirement for oxygen production is added, the conventional diesel engine still requires twice the energy needed to make a complete compression stroke.
Considering that I agree with you that the compressed gas will bounce back during the expansion stroke, much of the heat would have gone to the coolant during the compression stroke which is wasteful.
as for the engine speed, considering that it makes power in every revolution, i limit the engine speed to around 3000 rpm. With delivery of oxygen, water and fuel independent of engine speed and load, you can get peak torque even at 500 rpm and the peak torque will remain peaky even if you rev the engine further to 3000 rpm.
You will need a wide gear ratio CVT or AMT to really make a full use of the torque at speed as low as idling speed.
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