Direct injection
02-10-14, 10:43 PM
#1
Direct injection
So I'm working on something a little out if the norm. The motor is for my Rx2. I have a Renesis motor that has full PP intake and the stock side port exhausts. Ported of course. I'm 99% finished with my slide throttle bodies for it and have been tinkering with the idea of direct injection. I would place the injectors where the oil injectors normally sit in the older 13b's.
Now my question is, how would one control the direct injection? I have read that none of the current stand alones are capable of handling the direct injection without some kind of direct injector driver. I'm more of a machinist, welder, builder. I'm not too techy. Could someone explain to me what kind of ECU and or driver I would need to control the tricky direct injection?
Now my question is, how would one control the direct injection? I have read that none of the current stand alones are capable of handling the direct injection without some kind of direct injector driver. I'm more of a machinist, welder, builder. I'm not too techy. Could someone explain to me what kind of ECU and or driver I would need to control the tricky direct injection?
02-11-14, 10:59 AM
#2
There are standalones that will do GDI without external drivers. The price is steep though.
Technically, what you are talking about isn't considered direct injection. To achieve the benefits of direct injection, you would need to place the injector in the middle of the rotor at TDC.
With where you want to place them, you may be able to use regular port injectors and the associated hardware. Since the "cylinder" pressure is still low at that point, you may not need GDI levels of fuel pressure to make it work.
The down side to where you want to place the injectors is that you will not realize the benefits of true GDI.
Technically, what you are talking about isn't considered direct injection. To achieve the benefits of direct injection, you would need to place the injector in the middle of the rotor at TDC.
With where you want to place them, you may be able to use regular port injectors and the associated hardware. Since the "cylinder" pressure is still low at that point, you may not need GDI levels of fuel pressure to make it work.
The down side to where you want to place the injectors is that you will not realize the benefits of true GDI.
02-11-14, 04:11 PM
#3
^ What C. Ludwig said about the low pressure area of combustion chamber. I'm thinking of doing the same with my Renesis. I'm gonna put my injectors at the 12 o'clock position. I have some ideas and wanna see what kind of fuel economy I can get out of it. Even though it's not true direct injection, you still should save some fuel by not having it spray in a port where it collects on the walls.
02-11-14, 04:44 PM
#4
I build an engine with injection like you described a while ago,
Take the easy route, place a regular injector in the 12 o clock position of the rotor housing, you need to run higher than 3 bars of fuel pressure, more like 6 - 7 bars, and you need to use timed sequential injection. Also see if you can make the cut in the chrome liner of the rotor housing as small as possible, this will dramatically affect performance.
Take the easy route, place a regular injector in the 12 o clock position of the rotor housing, you need to run higher than 3 bars of fuel pressure, more like 6 - 7 bars, and you need to use timed sequential injection. Also see if you can make the cut in the chrome liner of the rotor housing as small as possible, this will dramatically affect performance.
02-11-14, 05:41 PM
#5
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^ What C. Ludwig said about the low pressure area of combustion chamber. I'm thinking of doing the same with my Renesis. I'm gonna put my injectors at the 12 o'clock position. I have some ideas and wanna see what kind of fuel economy I can get out of it. Even though it's not true direct injection, you still should save some fuel by not having it spray in a port where it collects on the walls.
Imo, in order for it to work you need the high pressure to get the atomization. When the fuel is injected conventionally it is done so right before the port opens so the fuel collects at the port opening and once it opens the rush of air helps to mix the fuel and air. You do not get that with the proposed injection above.
02-12-14, 09:06 AM
#6
Atomization was another concern I'm thinking of. Seems without the tumble effect of the port, its going to be hard to achieve a properly prepared charge. The rotary has a hard enough time creating a proper homogenous charge that is well packaged in the combustion chamber. In my head anyway, the extra turbulence in the port may help to promote a better fuel/air solution.
02-12-14, 01:19 PM
#7
Well, that makes me re-think the injector placement. I do want true direct injection. In the modern set ups they are using somewhere around 2000psi of fuel pressure with DI specific injectors and pumps. I would imagine with this, the atomization would be taken care of just fine.
I wonder where the best placement would be? Does the port timing effect best placement?
If dead center on the rotor housing radius is 0. Then how many degrees off center would have the most beneficial and true direct injection benefits?
I wonder where the best placement would be? Does the port timing effect best placement?
If dead center on the rotor housing radius is 0. Then how many degrees off center would have the most beneficial and true direct injection benefits?
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02-12-14, 05:21 PM
#8
Yes, with a high pressure gdi injector atomization is taken care of, but that's a much more difficult setup to build.
As for injector placement, I don't think port timing has a lot to do with it. You want the area near the leading spark plug to be saturated with fuel, so you need to spray towards that, which isn't really possible because of the fixed trochoid surface shape and the sort-of fixed rotor shape. With a 4-stroke engine the piston and combustion chamber can be shaped to create a nice pocket for the injector to spray at, but that's not really the case with a rotary.
For the direct injection engine I did I plugged up the trailing spark plug hole, and placed the injector roughly where the trailing plug was, but angled down, so it sprayes onto the rotor in the direction of the leading spark plug. The engine uses bosch HDEV 5.2 injectors, which operate at 200 bars. Like any other high pressure injector they do need a special circuit to function.
As for injector placement, I don't think port timing has a lot to do with it. You want the area near the leading spark plug to be saturated with fuel, so you need to spray towards that, which isn't really possible because of the fixed trochoid surface shape and the sort-of fixed rotor shape. With a 4-stroke engine the piston and combustion chamber can be shaped to create a nice pocket for the injector to spray at, but that's not really the case with a rotary.
For the direct injection engine I did I plugged up the trailing spark plug hole, and placed the injector roughly where the trailing plug was, but angled down, so it sprayes onto the rotor in the direction of the leading spark plug. The engine uses bosch HDEV 5.2 injectors, which operate at 200 bars. Like any other high pressure injector they do need a special circuit to function.
02-13-14, 08:00 AM
#10
Direct injection has/had been in development with Mazda, John Deere, Curtis Wright, Ingersoll Rand, and others for quite some time. There are a lot of technical articles written on it. Tons of info out there.
One thing to remember, and what I was trying to describe in my last post, was that atomization does not necessarily equal a homogenous mixture of fuel and air. Yes, you want the fuel/air mixture to be centered on the spark plug. But one of the biggest issues with the rotary engine is that the air distribution in the combustion "tub" is poorly coordinated. You end up with little pockets here and there. You can spray all the fuel right on the plug, but if a good portion of the air is located in the far reaches of the tub and not properly mixed with the fuel, you get a big fat misfire. You need the air to burn the fuel.
If you want to put a system together, we can supply the ECU with GDI drivers and rotary capability.
One thing to remember, and what I was trying to describe in my last post, was that atomization does not necessarily equal a homogenous mixture of fuel and air. Yes, you want the fuel/air mixture to be centered on the spark plug. But one of the biggest issues with the rotary engine is that the air distribution in the combustion "tub" is poorly coordinated. You end up with little pockets here and there. You can spray all the fuel right on the plug, but if a good portion of the air is located in the far reaches of the tub and not properly mixed with the fuel, you get a big fat misfire. You need the air to burn the fuel.
If you want to put a system together, we can supply the ECU with GDI drivers and rotary capability.
02-13-14, 05:47 PM
#11
The engine is currently up and running on the test stand (where that picture was taken), but it's still using the port injection for now.
02-13-14, 06:08 PM
#12
From what little I know about direct injection I was amazed at how lean you can safely run the engine. I first heard how hi the fuel pressure was I was worried about pumps burning up and leaning out the engine but this isn't a real consern.
.
Sadly I don't think automakers can take full advantage of GDI.
For example lets eliminate the throttle blades and controll rpm by adding and subtracting fuel. You have greatly reduce the engine brake caused by vacuum making the engine more efficient. But you will probably exceed set NOX limits do to the lean condition.
The only real advantage I see to direct injection is more acurte fuel timing do to faster computer and greatly reduced emissions do to fuel being injected after the intake port is closed eliminating overlap problems/ fuel going directly from intake to exhaust port.
.
Sadly I don't think automakers can take full advantage of GDI.
For example lets eliminate the throttle blades and controll rpm by adding and subtracting fuel. You have greatly reduce the engine brake caused by vacuum making the engine more efficient. But you will probably exceed set NOX limits do to the lean condition.
The only real advantage I see to direct injection is more acurte fuel timing do to faster computer and greatly reduced emissions do to fuel being injected after the intake port is closed eliminating overlap problems/ fuel going directly from intake to exhaust port.
Last edited by ghost1000; 02-13-14 at 06:10 PM.
02-13-14, 07:59 PM
#13
Or you will have terrible mpg because of the relatively low pressure injection and the really short time the fuel would have to atomize.
Imo, in order for it to work you need the high pressure to get the atomization. When the fuel is injected conventionally it is done so right before the port opens so the fuel collects at the port opening and once it opens the rush of air helps to mix the fuel and air. You do not get that with the proposed injection above.
02-13-14, 08:03 PM
#14
I build an engine with injection like you described a while ago,
Take the easy route, place a regular injector in the 12 o clock position of the rotor housing, you need to run higher than 3 bars of fuel pressure, more like 6 - 7 bars, and you need to use timed sequential injection. Also see if you can make the cut in the chrome liner of the rotor housing as small as possible, this will dramatically affect performance.
Take the easy route, place a regular injector in the 12 o clock position of the rotor housing, you need to run higher than 3 bars of fuel pressure, more like 6 - 7 bars, and you need to use timed sequential injection. Also see if you can make the cut in the chrome liner of the rotor housing as small as possible, this will dramatically affect performance.
I estimated everything you just mentioned. Even the small hole so you don't lose to much fuel/air charge through reversion around the hole. When I last had my 20b apart, I almost did the mod so I could have things in place and experiment later but, decided I would experiment on the Renesis instead.
02-13-14, 08:14 PM
#15
Any more details on this? Is this the new ecu you guys are developing or a modified ps2000? My 20b is set up in such a way that I use every single aux output. So I would need the 6 injector drivers to remain the same function without effecting the other outputs.
02-14-14, 04:05 AM
#16
Syvecs.
4 GDI outputs, 4 ignition outputs, 12 PWM outputs, 4 H-bridge outputs for DBW, 24 GP inputs, 2 knock inputs, 2 onboard EGT amps, onboard Lambda. Combine something like that with a 60-2 trigger and you'll have the processor power and accuracy to do GDI properly. Every unit is fully function enabled. So it's not like Motec where you pay extra for every option you want to unlock and use. Knock control, traction control, DBW, logging, flex fuel, etc.
That's the base GDI ECU. There are many other configurations for port injection and GDI. We'll be firing our first install this weekend. So far I'm liking the system but we have a long way to go with it.
4 GDI outputs, 4 ignition outputs, 12 PWM outputs, 4 H-bridge outputs for DBW, 24 GP inputs, 2 knock inputs, 2 onboard EGT amps, onboard Lambda. Combine something like that with a 60-2 trigger and you'll have the processor power and accuracy to do GDI properly. Every unit is fully function enabled. So it's not like Motec where you pay extra for every option you want to unlock and use. Knock control, traction control, DBW, logging, flex fuel, etc.
That's the base GDI ECU. There are many other configurations for port injection and GDI. We'll be firing our first install this weekend. So far I'm liking the system but we have a long way to go with it.
02-16-14, 01:36 AM
#17
Syvecs.
4 GDI outputs, 4 ignition outputs, 12 PWM outputs, 4 H-bridge outputs for DBW, 24 GP inputs, 2 knock inputs, 2 onboard EGT amps, onboard Lambda. Combine something like that with a 60-2 trigger and you'll have the processor power and accuracy to do GDI properly. Every unit is fully function enabled. So it's not like Motec where you pay extra for every option you want to unlock and use. Knock control, traction control, DBW, logging, flex fuel, etc.
That's the base GDI ECU. There are many other configurations for port injection and GDI. We'll be firing our first install this weekend. So far I'm liking the system but we have a long way to go with it.
4 GDI outputs, 4 ignition outputs, 12 PWM outputs, 4 H-bridge outputs for DBW, 24 GP inputs, 2 knock inputs, 2 onboard EGT amps, onboard Lambda. Combine something like that with a 60-2 trigger and you'll have the processor power and accuracy to do GDI properly. Every unit is fully function enabled. So it's not like Motec where you pay extra for every option you want to unlock and use. Knock control, traction control, DBW, logging, flex fuel, etc.
That's the base GDI ECU. There are many other configurations for port injection and GDI. We'll be firing our first install this weekend. So far I'm liking the system but we have a long way to go with it.
Hmmmmmm.
02-16-14, 01:05 PM
#19
Well, it's not my own engine, I did the machinework and build the engine for a technical university so I won't post detailed pictures of the engine's inside, but this picture showed up on the university's weblog, which kindoff shows what we did if you look closely:
The engine is currently up and running on the test stand (where that picture was taken), but it's still using the port injection for now.
The engine is currently up and running on the test stand (where that picture was taken), but it's still using the port injection for now.
Did the university ever report back to you on what they found with this engine? Curious how it worked out for them.
05-01-14, 06:53 PM
#23
Exhaust Manifold Leak
I think for max power it will not be worth the effort as at 10k rpm there is very little time for the fuel and air to atomize with direct injection. with port injection it is also better to place the injector at the trumpet instead then at the port. at least for WOT. for fast tip in it might cause a few cycles with lean mixture. good injectors like ID or ANSU atomize pretty well
in normal piston engine it was first tought to be beneficial to be able to run very lean and only run only a good mixture around the plug, so called stratified combustion. this way the engine could run WOT and the output could be controlled with fueling. just like a diesel engine, hereby reducing pumping losses
this worked very well for efficiency at part load, but the downside are NOx emissions..
at WOT the only thing that speaks for direct injection is that the volume taken up by the fuel in the charge is not there until the intake port is closed. this way the netto VE will be slightly higher. also the engine will probaly be more efficient at leaner air to fuel ratio if the injection timing and fuel distribution is so that there is little fuel in the area near the apex seals. as the mixture in this area doest take part in the combustion because the flame front is quenched there. so it is not beneficial to have any fuel there.
what seals are you using in the PP renesis? stock height or old style height?
in normal piston engine it was first tought to be beneficial to be able to run very lean and only run only a good mixture around the plug, so called stratified combustion. this way the engine could run WOT and the output could be controlled with fueling. just like a diesel engine, hereby reducing pumping losses
this worked very well for efficiency at part load, but the downside are NOx emissions..
at WOT the only thing that speaks for direct injection is that the volume taken up by the fuel in the charge is not there until the intake port is closed. this way the netto VE will be slightly higher. also the engine will probaly be more efficient at leaner air to fuel ratio if the injection timing and fuel distribution is so that there is little fuel in the area near the apex seals. as the mixture in this area doest take part in the combustion because the flame front is quenched there. so it is not beneficial to have any fuel there.
what seals are you using in the PP renesis? stock height or old style height?
05-02-14, 08:32 PM
#24
As of right now I plan to use the Rx8 style RA Super seals. But I have been debating with myself on milling the seal slots to use earlier taller seals. I just can't see any benefits in an NA application. Heavier seals mean loss in power.
I would love to go true direct injection, but the only thing keeping me out of going all the way is the tuning and electronic area. I'm much more skilled in the machining/fabrication area than I am in the techy area.
I would love to go true direct injection, but the only thing keeping me out of going all the way is the tuning and electronic area. I'm much more skilled in the machining/fabrication area than I am in the techy area.
05-02-14, 10:28 PM
#25
One of the potential advantages of the rotary is that the combustion geometry works well with stratified charge. There is a quite a lot of public information out there if you search through some of the old John Deere/ Curtiss Wright/ NASA stuff.
The idea is that with homogenous charge you have a constant A/F mixture throughout the cylinder, which means that fuel close to the rotor and housing walls does not burn completely, and the mixture near the spark plug is somewhat leaner than optimum. Conversely, with a diesel engine you have no fuel in much of the cylinder and liquid fuel at the injector. The areas with no combustion reduce the VE of the engine, and the areas where fuel is in large droplets do not combust well, which is also the cause of 'soot' in the exhaust.
Stratified charge gives you a 'best of both worlds' situation where you have well mixed fuel and air through most of the volume, but it is richer at the spark plug and very lean at the cylinder walls.
GDI piston engines are kind of quasi-stratified charge, because it is hard to make it work with the geometry and the movement of the piston/valves and a high swirl rate. Because of the sweeping motion of the wankel, it is easier to create a proper stratified charge.
To make a long story short, if you aspire to use GDI in a rotary, you should be attempting to make a stratified charge engine. Control of the injectors is not really a big deal. Motec has off-the-shelf GDI ECUs, as do most of the other big players at this point. The bigger issue is a fuel pump, as injection pressures are ideally very high, so an engine driven pump is a requirement. This means a drive mechanism is necessary. You could probably rob a pump from a newer GDI engine if you can figure out which one offers appropriate specs and how to interface with it. You also will need to find a way to control rail pressure, which can be done with a high pressure bleed valve if the pump does not have one built into it. Keep in mind that all of the high pressure plumbing for this system has to hold up to something like 200bar (~3000PSI).
Also keep in mind that that to get the best advantage out of this type of system, it would likely be necessary to modify the rotor bathtub. Still it might work OK just by poking an injector into a stock engine.
IMO using low pressure port type fuel injectors in the housings is a waste of time. There is no advantage over normal port injection. I do think there is a possibility for some good stuff with using GDi parts to make a stratified charge setup though. If someone wants to do the work and invest the money of building an engine with appropriate hardware, I can help you find and set up an ECU and control system...
The idea is that with homogenous charge you have a constant A/F mixture throughout the cylinder, which means that fuel close to the rotor and housing walls does not burn completely, and the mixture near the spark plug is somewhat leaner than optimum. Conversely, with a diesel engine you have no fuel in much of the cylinder and liquid fuel at the injector. The areas with no combustion reduce the VE of the engine, and the areas where fuel is in large droplets do not combust well, which is also the cause of 'soot' in the exhaust.
Stratified charge gives you a 'best of both worlds' situation where you have well mixed fuel and air through most of the volume, but it is richer at the spark plug and very lean at the cylinder walls.
GDI piston engines are kind of quasi-stratified charge, because it is hard to make it work with the geometry and the movement of the piston/valves and a high swirl rate. Because of the sweeping motion of the wankel, it is easier to create a proper stratified charge.
To make a long story short, if you aspire to use GDI in a rotary, you should be attempting to make a stratified charge engine. Control of the injectors is not really a big deal. Motec has off-the-shelf GDI ECUs, as do most of the other big players at this point. The bigger issue is a fuel pump, as injection pressures are ideally very high, so an engine driven pump is a requirement. This means a drive mechanism is necessary. You could probably rob a pump from a newer GDI engine if you can figure out which one offers appropriate specs and how to interface with it. You also will need to find a way to control rail pressure, which can be done with a high pressure bleed valve if the pump does not have one built into it. Keep in mind that all of the high pressure plumbing for this system has to hold up to something like 200bar (~3000PSI).
Also keep in mind that that to get the best advantage out of this type of system, it would likely be necessary to modify the rotor bathtub. Still it might work OK just by poking an injector into a stock engine.
IMO using low pressure port type fuel injectors in the housings is a waste of time. There is no advantage over normal port injection. I do think there is a possibility for some good stuff with using GDi parts to make a stratified charge setup though. If someone wants to do the work and invest the money of building an engine with appropriate hardware, I can help you find and set up an ECU and control system...