Why New Cars Are Using Both Direct & Port Fuel Injection

hello everyone and welcome in this video we're talking about why some companies are choosing to use both port and direct injection with their engines now way back in the day engines were carbureted then they moved on to port injection then they moved on to direct injection and now it's becoming increasingly common to see engines using both port and direct injection and the reason isn't all that simple there's actually quite a few advantages of doing this and so that's what we're going to get into in this video all right so let's start simple and then work our way through it so port injection meaning you are injecting that fuel before your intake valve before it enters that cylinder direct injection meaning you are injecting fuel directly into the cylinder now that fuel needs to change from a liquid to a gas needs to vaporize in order to combust so there's a little bit of a different strategy between port injection and direct injection port injection is going to be generally a much lower pressure that's injected in you're injecting into basically atmospheric pressure into this chamber right here unless it's turbocharged or has forced induction so you're injecting a low pressure fuel in there but there's plenty of time for that fuel to mix with the air around it because it's got the time that it's in that intake runner it's got the entire intake stroke and it's got the entire compression stroke that that air and fuel can mix with direct injection on the other hand your timing can vary so you may inject during the intake stroke you may inject during the combustion stroke either way you're gonna have less time for that air and fuel to mix versus port injection as a result of this you're going to use a higher pressure so that higher pressure will spray out a finer mist of fuel making it easier for it to vaporize with the air around it also because it's within the cylinder itself so if you're injecting into the combustion chamber at during the compression stroke you're going to have a high pressure that you're working against so a couple reasons why direct injection is going to have that high pressure but mostly to give it that really fine mist and that allows it to vaporize very quickly with the air around it now something very cool about fuel injection is that as you inject that fuel there's a cooling effect and so as that fuel changes from a liquid to a gas it cools the air around it and in doing so there's a different strategy between port versus direct because with port injection you're cooling that air before it enters that cylinder and so you're able to increase the amount of air that you bring into it it's almost kind increasing the charge effect especially with naturally aspirated engines so you're increasing the amount of air that you can enjoy that you can draw into the engine because you're cooling it with that fuel and in doing so you can bring in more air inject more fuel and make more power very cool with direct injection on the other hand there's a unique advantage to cooling just within the cylinder itself so you know that intake valve has perhaps closed but you're cooling the actual cylinder itself you're cooling the air within the cylinder there and by doing this you greatly reduce the likelihood for not so whereas before you're pulling in more air and fuel here you're not necessarily bringing in more air and fuel but you're reducing the chance that the air and fuel within this cylinder is actually going to encounter knock and so by reducing the chance of knock you can advance timing you can use more boost you can use engines with higher compression ratios ultimately you can make more power and you can operate more efficiently all right so now let's combine the two port and direct injection so here we have our simple cylinder right here we've got an injector in the top this could be in multiple locations the direct injector it could be into the side here below that intake valve and of course you have the port injector and so depending on where you are our engine wise our PM versus load is going to generally change the strategy of when are we using these and it differs company to company not generally speaking you're going to have port injection used at lower loads and at lower rpm as you can see in this region here you'll then start to use both port injection and Direction injection in these lower regions as well some companies will use both always some will choose to just use port injection and then as you get into those higher loads in higher rpm you want to reduce the likelihood of knock and so in doing so you're using just direct injection now some companies again will kind of spread where they use port injections so they may use both port and direct at low rpm and just direct at high rpm where they may use just port at low rpm direct and port injection at high rpm but either way that low to medium loading you're going for a better air fuel mixing because you've got that air and fuel mixing before enters the cylinder it's got more time to mix and so you're gonna have more stable combustion and more efficient combustion with that very even distribution of air and fuel and then the high load region and the higher rpm you want to maximize that cooling effect within the cylinder itself so that you can maximize power and you want that lowest chance of knock so that you can maximize power as well by doing those other things we talked about increased boost advance the timing use higher compression ratios that kind of thing now one interesting system that uses both port and direct injection is Toyota's d-4s and so they place their direct injection to the side of the cylinder so it's over here rather than right up on top of the cylinder and they have two different modes that this runs in which are pretty fascinating so there's a stratified mode which is used for efficiency stratified meaning different layers of air fuel ratios and then there's a homogenous mode which is used for power homogenous meaning an even mixture of air and fuel and so what happens with this stratified mode during the exhaust stroke so the exhaust valve is open the intake valve is closed they actually start injecting fuel so they're starting injection before your intake stroke actually begins they push out that exhaust the intake stroke begins and they stop injecting fuel from the port injector so that port injector first just during that exhaust stroke the intake stroke comes down then you have your compression stroke and right before that compression stroke starts to get up towards the top as it's getting closer to the top the piston itself actually has a contour in it and so the direct injection is injecting during that compression stroke late during the compression stroke and it's hitting that kind of contour of the piston and what that's doing is localizing a very rich air fuel ratio next to the spark plug which is in the top dead center and so during your power stroke what happens is during when you fire that spark plug you have a very rich area right beside the spark plug as a result of that direct injection causing that stratified layer that different layer of air fuel ratio so you have a relatively lean area for the most part that that's been purely mixed with all the air in there and then right directly beside that spark plug you have a rich your area and so what that enables you to do is ignite that leaner air fuel mixture around it so the spark plug is able to have consistent combustion because it's got a rich air fuel mixture Nick's next to it and then around it you have that leaner air fuel mixture which are able to ignite because that rich air fuel mixture has already started to expand and easier for all of that to combust so by doing this you're able to run a very lean mixture and you're able to have very efficient operation of your engine now Toyota also does something very similar with this where they have a cold start so during a cold start they will run this same strategy except a little bit more fuel with the port injector and the reason why you're doing that is to help heat up the catalytic converter first so what they're doing what they're saying is that by using these different areas of air/fuel ratios they're able to the timing of the engine and still have it operate smoothly and by retarding that timing you're putting less work in actually forcing the piston down because you're firing that spark plug later so think about it your Pistons coming down you fire that spark plug late combustion is still occurring and then you open up your exhaust valve so you have this really hot mixture which didn't do all that much useful work pushing the piston down and now all of that hot air is going out the exhaust so it's a way to have hot exhaust very quickly heat up the catalytic converter and get the emission system running very quickly rather than if you were to simply run it like a normal cycle okay so what if you want to make power well that's where they have this homogeneous mode right here so during your exhaust stroke same as before you're going to start injecting that fuel while your intake valve is still closed then you get up to the top you begin your intake stroke pulling that piston down and now your direct injector is going to be injecting fuel directly into the cylinder your port injector has stopped so you have plenty of time for all of this air and fuel to mix because you're injecting the direct injection during the first half of that intake stroke and you're injecting beforehand before that intake valve even opens with the port injector so you have this nice rich air fuel mixture that's evenly distributed throughout that cylinder and you compress that all together and then you have of course maximum power because you're burning the maximum amount of fuel and you're able to you know have that nice even mixture there which results in quick combustion so maximizing power through the air fuel mixture through using a rich air fuel mixture and through having it evenly distributed throughout the piston cylinder device and finally we get to carbon deposits and this is kind of the hush hi industry secret we don't talk about this and you know I've asked a good number of engineers who work for companies which have both port and direct injection engines and what a lot of them will say is when I ask why do you use both direct injection and port injection they will say all of this other other stuff and all of this other stuff is certainly valid and perhaps that is the only reason why they do it they will never tell me I have not had an engineer working for an automotive company tell me that they use this in their engine because they want to reduce carbon deposits so there are direct injection engines out there which don't have carbon deposit problems but it is not necessarily the norm and so it is more likely that port injection engines will have fewer carbon deposits on the intake valves and so why is this well if you look at an engine you have multiple systems going on that will affect build-up on these intake valves so you have your positive crankcase ventilation system and so you're going to have blow-by when you have combustion occur some of that combustion kind of slips past these pistons and it pressurizes your crankcase and so you have this positive crankcase ventilation system in order to vent that positive pressure into your intake and so in doing so you'll have some of the byproducts from combustion that blow by going into your intake and you'll also have that oil mist so you've got that crankshaft which is turning that oil you've got this oil mist kind of sitting in that crankcase so that oil mist and those combustion byproducts the blow-by will re-enter your intake tract and hit your intake valve and they can stick to it burn to it and form these deposits you also have an exhaust gas recirculation system so that exhaust gas recirculation system used for emissions will send some of that exhaust those combustion byproducts and contaminants back into your intake and then of course you also have your valve guides so the oil itself the engine oil itself can slip down through these valve guides and onto the valves and cause deposits to form so there are many ways in which deposits can accumulate and form on these intake valves and with a port injection engine you're spraying that fuel and that fuel spray will end up hitting that valve and removing those deposits from the valve there's actually specific fuel additives generated specifically just to remove those deposits from the intake valves and so you know a port injection system is a great system in order to keep those deposits very clean now I saw a study published in sae in 2011 and it was saying that they were seeing more than 10 times greater amounts of these different chemical elements here that we have so we're going to test my chemistry really quick calcium moe I believe is the technical term zinc phosphorus sulfur I don't know what Moe is I didn't do so hot in chemistry regardless they saw 10 times increase of these different elements as deposits on the intake valves and so there is a significant difference there studies showing that direct injection engines tend to have more deposits than port injection engines and there are certainly engines out there which are direct injection which suffer from carbon deposit problems on the intake valves so thank you all so much for watching if you have any questions or comments of course feel free to leave those below

Channel: Engineering Explained

Views: 275,497

Keywords: fuel injection, direct injection, port injection, gasoline, shell, chevron, bp, gas prices, gas price, premium gas, 87 octane, 91 octane, 93 octane, best gas, cheapest gas, toyota d-4s, toyota, honda, ford, chevy, subaru, mazda

Id: 66C4YIiwRbM

Length: 12min 6sec (726 seconds)

Published: Wed Feb 13 2019