Recent comments in /f/askscience

ExoticSwan8523 t1_j1f163t wrote

Reply to comment by MadJackandNo7 in Why do teeth have nerves? by ileiskit

Ever bit your tongue before? If yes, then the nerves in both your tongue and teeth are not 100% effective at preventing you from biting your tongue. Now take away all of your teeth's nerves, and you're going to increase the likelihood of biting your tongue with less nerves.

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yurikovski t1_j1ez3ef wrote

Reply to How does the non-CO2 emissions of an external combustion engine compare to an internal combustion engine? by Past_Self_4845

The authoritative source on this is probably the US EPA AP-42 list of emission factors.

You could compare natural gas combustion in external vs internal. These are in terms of pounds of pollutant per mmbtu of fuel input.

In an uncontrolled natural gas turbine, you get 0.32lb/mmbtu NOx and 0.082lb/mmbtu CO. In a 4-stroke internal combustion engine, it's 4.08lb/mmbtu NOx and 0.317lb/mmbtu CO.

In a large boiler, it's 0.19 lb/mmbtu NOx and 0.082lb/mmbtu CO.

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magungo t1_j1etk9b wrote

Reply to How does the non-CO2 emissions of an external combustion engine compare to an internal combustion engine? by Past_Self_4845

The increased Nitrogen oxides in internal combustion is due to the compression phase of these motors. Given enough heat and pressure the Nitrogen from the atmosphere can be involved in more chemical reactions. Usually Nitrogen doesn't want to react much but we are forcing it to. This is why Diesel engines with higher compression ratios produce more Nitrogen oxides. As for CO that is more to do with incomplete combustion and is getting less and less with better engines running lean fuel mixtures and more computer control. In theory the Catalytic converter should be reacting most of the CO into CO2 but it's not going to be 100%.

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PerspectivePure2169 t1_j1eiotd wrote

Reply to How does the non-CO2 emissions of an external combustion engine compare to an internal combustion engine? by Past_Self_4845

The answer is going to depend tremendously on the fuel used, the conditions of burn, and any stack scrubbing or recapture equipment present.

Internal combustion engines have a starting advantage in that they tend to burn "cleaner" fuels - especially in the past. But external combustion systems have the advantage of larger plants and (generally) more space and attention to efficiency and emissions.

Looking at coal alone, there's a lot of variation among coal fields, as well as categorical differences between soft brown coal and anthracite.

But in any case, a cleaner starting fuel gives less to mitigate at the stack.

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mrwolfisolveproblems t1_j1ehkcm wrote

Reply to comment by FRCP_12b6 in How do fusion scientists expect to produce enough Tritium to sustain D-T fusion (see text)? by DanTheTerrible

If an EV battery is so degraded it can provide a few hours of runtime in a car what meaningful use will it have to the grid? Has anyone actually tested this at reasonable scale beyond a simple demonstration? Who is going to pay for the infrastructure to connect all these old batteries to the grid? That grid storage argument is just thrown out there for PR. It would take decades to get off the ground and we’re going to have millions of dead battery packs in 10 years.

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man_o_brass t1_j1egnvb wrote

Reply to Can the Doppler effect make sounds inaudible by shifting frequencies out of human hearing range? Or vice versa? by IonnoFry

Absolutely, although in practice, the frequency of the sounds would need to be fairly close to the limit of human hearing so that you wouldn't need to be going very fast. At very high speeds required for very high doppler shifts, wind noise would likely drown out what you were trying to hear.

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