The future of the engine as we know it 1

[franzh]

I normally run like crazy when someone asks me questions about a "new" engine, but when one of my directors asks me to evaluate a "new design" design, my knees shake. That happened this morning.

We have seen free pistons, opposed oscillating pistons, scotch yoke pistons, toroidal blocks, ball valves, sliding sleeves, and tons of other combinations. Strangely, or not so strangely, none of these has ever reached any significant success. The old, inefficient Otto cycle engine still hangs around. With the exception of sealing refinements and air-fuel metering, almost nothing has changed in 100+ years, not including OHC engines which is a refinement, or phased cams, also a refinement, or exhaust aftertreatments, which is not a refinement, but an attempt at fixing an engine inefficiency.

I wonder how long it will take before something else pops up and takes a reasonably strong stand against the tried and true engine design?

Lets look at the true IC engine replacement, not hybrids (although I feel that is where we are heading for the next 25 years). Turbines are nice but not practical for a number of reasons.

When we look at H2 as a potential fuel, it still uses the Otto cycle engine as a base, only the fuel has changed. Are we really gaining anything on the engineering side? I recognize the significant advantage on emissions, but fuel transport, storage, and infrastructure have still to be perfected.

Any ideas, fellow engineers?
Franz


eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[EdDanzer]

Disruptive engine and drivetrain technology requires clean sheet designing. First you must understand the drive cycle. For most city driving people, this is stop and go at lower speeds. The actual torque/HP required at the wheels is not well known. Regenerative braking is a must. This is difficult because braking energy is 2 to 3 times accelerating energy for a shorter time. Most variable speed electric drives are under 80% efficient average over their rpm range during regeneration, and under 87% efficient average over their rpm range.
Since burning fuel releases heat, converting that heat to power is a simple, yet complex problem. The pressure and expansion from combustion in gas and diesel piston engines is used to rotate a crank, swash plate, or rotor. All these current systems have an intake stroke equal to the power stroke. Sterling engines and steam require heat to be to be transferred through metal walls.
The difficult problem with expanding a gas is the pressure becomes lower the longer the expansion takes place, so extracting that energy becomes more difficult and less attractive. (Lower power to weight ratio)
My solution is to decouple each cylinder, so only the number required to propel the vehicle are firing, and have them run at the optimum piston speed. Then to extract maximum heat to expansion, shortly after the fuel is burnt, inject water to provide a more efficient expansion fluid. This requires the power stroke to be longer than the intake and compression, so a linear engine is required. It seems the pumping losses for a 4 stroke are less than a 2 stroke, so this is the direction I’ve chosen.
Having built and tested the basic design, the next problem is converting this motion to wheel torque. The required energy is high, and the densities for mobile application make hydraulics the best choice, yet there are neither hydraulic valves, or motor designs are available to meet these requirements yet.
For more information visit:

http://www.dehyds.com/