Americans Have No Idea How Much Fuel Idling Uses

hello everyone and welcome how much fuel do you think it takes to start up an engine another way of asking this question how much time does it take an idling engine to use the same amount of fuel required to start up an engine now if you knew the answer to this question you could potentially save fuel if you knew how long you were going to be sitting in a stoplight or something like that perhaps a train is crossing by and you could also answer whether or not start stop systems in modern cars are actually doing anything now according to a study published in the journal of energy policy they asked 1300 u.s drivers how long they thought it would take before it was more beneficial to shut an engine off rather than let it idle and the average response amongst 1300 participants in that study was 3.6 minutes the good news is we don't have to guess or ask our uncle or cousin or whoever about how much fuel an engine uses while it's idling it's well researched the data is out there you just have to go and read it and so this is how much fuel a small four-cylinder engine will consume while idling for 3.6 minutes and this is how much fuel it actually takes to start that same engine up small four-cylinder engine so this is what the average american thinks it takes to start up a four-cylinder engine and this is how much fuel it actually takes to start up a small four-cylinder engine now if you're embarrassed because you're an american and you had no clue how much it takes to start up an engine don't worry i'm sure plenty of the rest of the world also didn't know how much fuel it takes to start up an engine i mean i didn't know wait i'm american so no more guessing in 2004 a study published in the journal of sae sought to find out whether or not engine start stop systems actually improve fuel economy the study took two identical cars both with 1.5 liter four-cylinder toyota gasoline engines and they equipped them with fuel flow meters so they could measure the fuel going into the engine being consumed now to get a baseline measurement of the engine's idling fuel consumption they idled both vehicles in both park and then in drive for 90 minutes and measured how much fuel they used during those 90 minutes you then do a little bit of division and you come down to the fuel flow rates for an idling engine so this is how much fuel an idling 1.5 liter engine uses in just 10 minutes so if you had six of these that would tell you how much it uses in an hour so it's about .63 liters or about one sixth of a gallon that this idling engine will use every hour and of course if the displacement of that engine is larger then it's going to use even more than this it's also interesting to note that there really wasn't much of a difference between having the car in park and having the car in drive as far as how much fuel it was consuming while idling so next they wanted to find out how much fuel does it take to start up an engine and so in order to do this they started and stopped the engine a ton of times basically what they did is they did they started they stopped it they started they stopped it until it had used the same amount of fuel that the engine had used while spending 90 minutes idling from there it's a pretty simple equation you take the total amount of fuel used and you divide it by the number of times that you started the car and that's where they came up with the 1.1 to about 1.2 milliliters of fuel required in order to start a 1.5 liter engine okay you're still following right so if you take the amount of fuel required to start up the engine and you divide it by how much fuel the engine uses while idling in fuel per second then you get how many seconds does this engine have to idle in order for it to be more beneficial to instead simply shut it off so if you take 1.2 and you divide it by 0.171 cc per second which is the fuel rate at idle then you get about seven seconds so if this engine is idling or a 1.5 liter four-cylinder engine is idling for seven seconds if it's going to idle for any longer it's more beneficial to simply shut it off and then restart it once traffic is moving again now i'm sure this is where plenty of your heads start exploding you say jason it's not safe to turn your car off in traffic or i need my ac look i'm not telling you how to live your life or drive i don't really care what you do what i'm telling you is just the data behind fuel consumption so if you want to save fuel if that was your only goal how you drive is your business do whatever you want to do but just letting you know after you let that engine idle for longer than about seven seconds your wasting fuel had you just let it shut off so that's the justification for a lot of the systems out there which do have start stop which by the way they have completely different starters which are used to start those up so they're built for many more repetitions many more starts and stops they're designed for it from the start it turns out engineers are capable of thinking about these things knowing that hey if you use a starter a ton of times you probably need to design for it they do it don't worry about it so if you do want to save fuel using a start stop system what this is showing is that if your car is shut off for longer than seven seconds then it could be beneficial wait come back i see that mine wandering on me again now you're thinking jason but this isn't a 1.5 liter engine so surely in a larger engine you know maybe that doesn't it maybe it's longer than seven seconds well you know that could be but here's the thing the larger engine is not only going to require more fuel to start up it's also going to require more fuel to idle so the ratio may remain somewhat similar so estimating about seven seconds eight seconds nine seconds isn't that crazy to do because as the engine gets larger it takes more fuel to start up it takes more fuel for it to idle okay now we get to the final part of the study and this is really cool so what they wanted to find out was whether or not engine start stop systems actually save any fuel and so what they did is they took both vehicles they equipped one of them with a start stop system and then they had the other always running when it came to a stop so the engine would idle at a stop versus the other one would shut off whenever it came to a stop so they took both of these vehicles and they drove the same route in four different ways so four different types of traffic so it was you know real world driving uh just using real traffic and they just put one car right behind the other and this is city driving so we don't have to worry about aerodynamics playing a role here the front car you know towing the car behind it uh the the speeds are very low so real world city driving test to show you know does this actually save you any fuel uh you know when of course start stop systems are designed to save you fuel in-city driving and so the cars are right behind each other they're driving the exact same route and the exact same traffic and they range from light traffic to heavy traffic and what they found is that in all four of those scenarios the car with start stop actually got the best fuel economy and so it ranged from about four percent better to as high as 8.7 better fuel economy with the car that did have start stop equipped okay so what have we learned well first of all it takes very little fuel in order to actually start up your car just about 1.2 milliliters to start up a 1.5 liter four-cylinder engine especially when comparing that to how much fuel an engine uses while idling we also learned that if your engine is idling for longer than about seven seconds you're actually starting to waste fuel and finally real world city driving shows that you can actually save about four to eight point seven percent in fuel economy by using a start stop system versus just letting the engine idle when you come to a stop now of course feel free to let me know in the comments below why everything about this video is nonsense thank you all so much for watching

Channel: Engineering Explained

Views: 3,409,105

Keywords: engine idle, fuel economy, fuel consumption, good gas mileage, gas mileage, how much fuel, does engine start stop work, start stop technology, stop start engine, engine start stop, how much fuel does idling use, how much fuel to start a car, car starter, starting a car

Id: dFImHhNwbJo

Length: 7min 14sec (434 seconds)

Published: Wed Sep 05 2018