Sonic effects

[Desmoguzzi]

I would Like to ask to Experts questions about sonicity. I could not found answers somewhere else maybe here someone know or can address me to any source of information.

Let's suppose that in One section of intake Port the air reaches the sonicity Speed then:

- what happen to the fuel mixed in the air? It Will be further atomized or It Will condensate in liquid deposit on the Wall of the Port?
- what happen to the pressure waves when they cross the sonic section? Will they be stopped or they Will pass trought the Sonic section?
- Will the Sonic Speed in the section create shock waves Like when a jet cross the Speed of sound? If yes what kind of role they play on the induction cycle?

Thanks in advance

[swampbuggy]

This is a question for Darin Morgan or equal . Mark H.

[Desmoguzzi]

This is a question for Darin Morgan or equal . Mark H.

Then Hope he Will answer!

[LotusElise]

- what happen to the fuel mixed in the air? It Will be further atomized or It Will condensate in liquid deposit on the Wall of the Port?
- what happen to the pressure waves when they cross the sonic section? Will they be stopped or they Will pass trought the Sonic section?
- Will the Sonic Speed in the section create shock waves Like when a jet cross the Speed of sound? If yes what kind of role they play on the induction cycle?

That would be only, if any, possible in highly boosted supercharged engines (not possible within turbocharged engines), where during exhaust stroke enough low cylinder pressure can be created. But due to the filling the Mach 1 condition can't endure for long, if any. I assume top fuel engine will experience those conditions for some degrees crank angle. But other than stationary the setup is limited due to valve lift. Mach 1 condition can be reached at intake valve at very low lifts, even in highly effective NA engines when header has a very good design. Cylinder pressure need to be go down below critical pressure ratio (p_cyl/p_valve backside <= 0.528/1). Supercharged, this can endure longer than a few degrees crank angle, e.g. top fuel engines.

Other than in stationary sonic flow regimes this here is a pure dynamic one. It compares to those of sudden, fast emptying pressure loaded sources (e.g., an air-filled boiler at over-critical pressure-ratio to outlet conditions) into atmospheric conditions. But other than there, the acceleration phase will take much longer in a relative perspective. Thence the inflow process is quite dynamic, inertia plays the major role, that means fuel and air will have separate parties, so to say.

The pressure oscillating back and forward doesn't play a significant role in such a flow regime. The critical pressure ratio is e.g. in air higher than 1.89/1 or vice versa 0.528/1. If there would be a fixed and consistent Mach 1 plane, it would equalize the velocity/mass flow. But the Mach 1 plane is likely only existing at the valve curtain at low lift, after the pressure increases in the cylinder and the valve moves up it is very likely that no supercharger system would be able to keep up the Mach 1 condition, engine designer would always adapt the valve size so that Mach 1 has the lowest chance to hinder flow.

If Mach 1 can be reached at valve curtain area, you can assume shock waves get generated in the cylinder. But again, the situation is highly dynamic and the Mach 1 situation is short so that the effects likely can be neglected.

I was involved in a two-staged turbochargerd pre-chamber lean burn engine development with almost 100 psi of boost. We never saw an breakup in the boost-power-correlation, which was almost linear. If compression shock would happen, that correlation would not fit.

[Desmoguzzi]

- what happen to the fuel mixed in the air? It Will be further atomized or It Will condensate in liquid deposit on the Wall of the Port?
- what happen to the pressure waves when they cross the sonic section? Will they be stopped or they Will pass trought the Sonic section?
- Will the Sonic Speed in the section create shock waves Like when a jet cross the Speed of sound? If yes what kind of role they play on the induction cycle?

That would be only, if any, possible in highly boosted supercharged engines (not possible within turbocharged engines), where during exhaust stroke enough low cylinder pressure can be created. But due to the filling the Mach 1 condition can't endure for long, if any. I assume top fuel engine will experience those conditions for some degrees crank angle. But other than stationary the setup is limited due to valve lift. Mach 1 is at intake valve at low lift in highly effective NA engines when header has a very good design. Cylinder pressure can go down below critical pressure ratio (p_cyl/p_valve backside <= 0.528/1)

Other than in stationary sonic flow regimes this here is a pure dynamic one. It compares to those of sudden, fast emptying pressure loaded sources (e.g., an air-filled boiler at over-critical pressure-ratio to outlet conditions) into atmospheric conditions. But other than there, the acceleration phase will take much longer in a relative perspective. Thence the inflow process is quite dynamic, inertia plays the major role, that means fuel and air will have separate parties, so to say.

The pressure oscillating back and forward doesn't play a significant role in such a flow regime. The critical pressure ratio is e.g. in air higher than 1.89/1 or vice versa 0.528/1. If there would be a fixed and consistent Mach 1 plane, it would equalize the velocity/mass flow. But the Mach 1 plane is likely only existing at the valve curtain at low lift, after the pressure increases in the cylinder and the valve moves up it is very likely that no supercharger system would be able to keep up the Mach 1 condition, engine designer would always adapt the valve size so that Mach 1 has the lowest chance to hinder flow.

If Mach 1 can be reached at valve curtain area, you can assume shock waves get generated in the cylinder. But again, the situation is highly dynamic and the Mach 1 situation is short so that the effects likely can be neglected.

I was involved in a two-staged turbochargerd pre-chamber lean burn engine development with almost 100 psi of boost. We never saw an breakup in the boost-power-correlation, which was almost linear. If compression shock would happen, that correlation would not fit.

Dear Lotus, thanks for the very clear answer.

Full Sonic condition maybe It Is too severe condition. Often the minimum section in intake Port Is sized to have Max 0.5/0.6 mach. Let's suppose then to have on a section of the intake Port 0.5/0.6 mach or in other Word a choke condition, what would be in this case the answers tò my questions?

Thanks again.

[LotusElise]

Full Sonic condition maybe It Is too severe condition. Often the minimum section in intake Port Is sized to have Max 0.5/0.6 mach. Let's suppose then to have on a section of the intake Port 0.5/0.6 mach or in other Word a choke condition, what would be in this case the answers tò my questions?

For NA engines that Mach numbers are maybe reached in the throat of the port at max valve lift for a very short moment. On average it is quite lower.

The throat concentrates flow and liquid droplets, which of course lead to separation of droplets as they don't follow the expansion and flow direction change as the gaseous part can (applies for vaporized fuel and air). Fuel separation also happens at the liner, the higher the velocity, the flatter the port angle before short turn and the steeper the tangential line of seat and short turn compared to the port axis. These ports may need a more advance EOI to get more fuel vaporized before IVO.

Wet flow testing is not well developed in OEM areas or the European race scene. The US race scene has much more focus on that since the late 70'ies (and later reviveled by e.g. Joe Mondello's Superflow wet flow approach). Fuel ramps and stuff, incorporated into the port supply wall film separation to keep the droplets in the air flow. The choke velocity plays a role on that.

I would like to keep the discussion on the general influence of fuel separation, but the top liner doesn't apply to that.