Ok.For compressible fluids, A1V1=A2V2 will not hold.But in carburetors, till the throat they apply the continuity equation for incompressible fluids(air is the fluid). The throttle valve will be below the throat. At the throttle valve(air fuel mixtureis the fluid), in most of the books they would not apply A1V1=A2V2.Does air becomes compressible because of fuel addition?FactChecker said:
Air is always compressible. In some circumstances, the equations for incompressible fluids may give a good enough approximation.Mohankpvk said:
The addition of fuel, with evaporation and cooling, may have an effect. I am not familiar enough with this subject to say more.
So, the continuity equation doesn't hold for a throttle valve (i.e. when applied for two points one before and the other after the valve along the flow) because it alters the nature of flow by sudden reduction in cross sectional area.Is this conclusion right?cjl said:
I don't think that is what he is saying, but you bring up a good point that may be very significant. All the Bernouli-related results are talking about smooth, steady-state flow. A throttle that introduces turbulent flow is completely different.Mohankpvk said:
Ok. So the continuity equation cannot be applied for two points one before and the other after the valve along the flow, because it alters the nature of flow(makes the flow turbulent) by sudden reduction in cross sectional area.Is this conclusion right?FactChecker said:
I would say that it is not just the reduction in the cross sectional area -- it's the non-aerodynamic way it is done. But otherwise, I think that is right. That being said, I would defer to those who know more about this subject.Mohankpvk said:
No, it is because the density has to be present in the relationship. If the density is present, the continuity equation will apply even if the flow is turbulent. The continuity equation (in the for I specified) will be correct at steady state provided there is no additional gas added to the flowMohankpvk said:
My thinking is that turbulent flow through a restricted area would have flow forward, backward, and crosswise, so that it would be equivalent to a net non-turbulent flow at a lower velocity. (or through a smaller area) -- No, I don't think either of those can be correct.Chestermiller said:
I have no idea what this means. At each and every cross section, if the flow is steady, irrespective of whether it is turbulent, the mass flow must be ##\dot{m}=\rho v A##, where ##\dot{m}## is the (constant) mass flow rate, and v is the normal velocity averaged over the cross section.FactChecker said:
How can steady flow include turbulance? They are not compatible.Chestermiller said:
Ok. I'll buy that. I have gotten well out of my area of knowledge and will bow out.cjl said:
More important is the time scale for the turbulence. We chemical engineers learned our fluid mechanics from the classical text Transport Phenomena by Bird, Stewart, and Lightfoot, and they were very clear in emphasizing that, if the flow is averaged over the very short time scale typically encountered with turbulence, it is manifestly valid to consider the flow steady.cjl said:
Ok.But if mass flow rate is constant, how will the valve reduce the rate of air fuel mixture flowing through it?Chestermiller said:
When I said that the mass flow rate is constant, it was implicit that I was talking about "constant with respect to spatial position within the control volume." When you use a valve to control the mass flow rate, you are changing the mass flow rate by increasing the resistance to flow (but this only affects the mass flow rate with respect to time, not spatial position at a given mass flow rate). The speed of the piston movement can change by applying more or less "oomph" to the piston (higher force).Mohankpvk said:
I think that I should have added incompressible and/or steady-state.FactChecker said:
A throttle valve, also known as a throttle body, is a component of an engine's air intake system. It is responsible for controlling the amount of air that enters the engine. The throttle valve works by opening and closing to regulate the flow of air, which in turn controls the engine's speed and power.
A carburetor is a device that mixes air and fuel in an internal combustion engine. Unlike a throttle valve, a carburetor controls both the air and fuel mixture that enters the engine. It does this by using a series of small tubes and jets to create a precise ratio of air and fuel for optimum engine performance.
In terms of efficiency, a throttle valve is generally considered to be more efficient than a carburetor. This is because a throttle valve allows for better control and adjustment of the air to fuel ratio, resulting in more precise combustion and better fuel economy.
It is possible for a car to have both a throttle valve and a carburetor, but it is not common. Most modern cars use fuel injection systems, which have replaced the need for a carburetor. However, some older cars may have both a throttle valve and a carburetor as part of their engine's air intake system.
When it comes to performance, a carburetor is generally preferred over a throttle valve. This is because a carburetor can provide a more precise air and fuel mixture, resulting in better engine performance and power. However, with advancements in technology, fuel injection systems have become even more efficient and are now the preferred choice for high-performance engines.
