Fuel Injectors

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Injector Table


Impedance

There are two common coil resistance types: High impedance ( Saturated) and low impedance(Peak and Hold). The high impedance types are generally used by original equipment manufacturers (OEMs). The low impedance units are used on performance and some mass produced turbocharged cars. The high impedance are used on the majority of mass produced cars.

Peak and Hold injectors are generally copper wound, while Saturated coils are brass wire wound.

Peak and Hold = 2 -4 ohms

Saturated = 12 - 16 ohms

Generally the lower the resistance the faster the action, but the ECU drivers must be impedance matched and capable of handling the current draw.

Performance

Peak and hold injectors are current devices and typically draw about 4 amps when fired. Often a ballast resistor is included in series with the coil to limit the inrush current. Once the armature is engaged the current drops back and holds at about 1 or 2 amps. They have better actuating response and can handle higher fuel pressures. They will deliver fuel faster than saturated types and are very precise in comparison. Typically they react over 1 millisecond faster than the saturated types. This is significant when you consider the injector may only open for 8 or so milliseconds at low revs. A separate 6 amp plus output driver from the ECU is required for proper operation and they are ideally suited for sequential firing.

Saturated injectors are voltage devices and have a ramping type operation, compared to the square edged response of the Peak and Hold. They are by far the most common injector, because of OEM applications requiring cost minimisation and simplicity. They are particularly suitable for batch fire applications where only one or two outputs from an ECU are required.

The minimum cycle time Peak and Hold is about 2 milliseconds for pintle type injectors and 1 millisecond for disc type. The minimum for saturated types is about 2.5 milliseconds for pintle and 2 milliseconds for disc.

Spraying Fuel

The trick is to have an injector that will deliver the fuel into the combustion chamber in a perfect stoichiometric mix. The hard part is making sure its atomised just enough without clinging to the intake port walls and not so underatomised that is remains a fluid. When the valves are overlapping a highly atomised vapour will tend to be blown back up to the plenum by residual exhaust gas, so the mixture needs to be dense enough to hang around the intake port as the pot vacuum comes into play, but at the same time not cling to the walls of the port.A smaller cone pattern would tend to be more desirable in a race situation for a more directed spray that is less likely to be entrained in gas pulsations going back out the intake.

Some performance engines do not atomise the fuel, rather streaming the fuel around the back of the intake valve just prior to opening. The latent heat of vapourisation from the intake manifold results in a desirable denser fuel/air mixture and a cooler manifold itself.

There are a half dozen metering methods: including pintle, disc, swirl plate, diffuser/ pintle, ball and socket, radius rod. The pintle are generally Bosch and Nippon Denso. Pintles tend to change atomisation quality as fuel pressure increase. Dual diffuser/pintles maintain spray quality at higher fuel pressures, have a wetter and directed cone pattern. Disc type injectors are highly regarded for continuity of pattern under varying pulse widths and fuel pressures.

Pintle injectors have an effective range up to 85% opening while disc is about 92% opening. The swirl type injectors (mitsubishi) are used in direct injection engines to create a dense stratified fuel mixture at the top of the combustion chamber, resulting less fuel requirement.

There are three main types of injection method:

Throttle body injection (TBI) was the early method, where a throttle body and injector(s) replaced the carburettor. The fuel was sprayed into the intake manifold and the resultant mixture drawn in through the intake runners.

The next step was the currently popular multipoint or multiport fuel injection (MFI). The fuel is sprayed into the air stream for each individual intake port, for final mixing in the combustion chamber. The manifold no longer needs preheating to aid in vapourisation, although many manifolds with this system still have water circulating, especially where the heads are transitional carburetted models.

Direct injection is the new system being adopted. It allows for leaner mixtures (40:1) at low load, thus resulting in tangible savings in fuel consumption. . The injectors produce a stratified fuel vapour that is concentrated around the spark plug for ignition. The incoming air actually bypasses the injector (which is late firing) as it enters the cylinder, rebounds off the cup shaped piston and squeezes the straified fuel vapour rich mixture up against the spark plug area.

Duty Cycle

This is simply the ratio, usually expressed as a percentage, of the injector on time (pulse width) compared to the available cycle time. On a four stroke engine the cycle time is over 720°. So for example, if an engine is running at 5000rpm the time for one complete cycle is 120/5000 = 24 milliseconds.

Now the thing to remember is that an injector has an hesitation before opening on signal to do so. This is because the coil needs to build enough flux density to actuate the armature. This time can be anywhere from 0.85 msec to 2.0+ msec. So this effectively reduces the available cycle and rest time of the injector.

So lets say the signal pulse width for our 5000rpm engine is 16 msec and our injector has a deadband of 2 msec. The effective duty cycle is 16/(24-2) = 72.3%.

Testing

The ASNU (pronounced as new) tests are the most common:

the machine has the algorithms built in to conduct the testing. The common method is "F' cycle.

If we take Scarface's test results for GTti injectors:


Posted: Mon Jan 19, 2004 5:20 am Post subject:

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Nippon Denso L-Jet
95500-1610(Red)

ASNU Injector Service Report

Inj.No. Flow Rate ml Pressure Setting PSI

1 69 36
2 69 36
3 69 36

By the way i can highly recommend getting this done as it made a big difference.

we have no way of knowing what test was performed, although members have stated the injectors are 295cc/min. If it was an F test (e.g. 36millisec@2500rpm) and the results are over a 15 second period, then the injectors would be around the 320cc/min mark. If it was D test the injector would be a full flow static test, but it is difficult to see injector variations due to the small time frame involved, in this isntance the injectors would be approx 4 x 69 = 276cc/min..

Unfortunately the tests have changed with different machines, so an F test on one model may be different to another.

Basically the machine measures the time it takes to part fill a graduated test tube (eg 100cc or 130cc tube) with a fuel substitute (e.g.n-Heptane)at a given duty cycle and fuel pressure.

Injectors are universally rated in cc/min or lbs/hour. To convert cc/min to lbs/hr divide by 10.5. assuming a specific gravity/volume of the fuel is nominally 0.73ish.

Sizing

Tricky situation with injectors is that its desirable to have the shortest possible pulse at full load (to prevent unburnt fuel loss during valve overlap), but at the same time not having such a big injector that the low load fuel map requires a pulse that puts it under the Minimum Linear Pulse Time (MLPT).

If you imagine a linear relationship between zero flow and full load flow, there will obviously be a deviation from that line in the real world, because of the annular shape of the needle and seat, valve bounce/ hysterisis plus as opening becomes longer the needle isn't fully closed before the next open pulse signal is recieved. The shortest pulse time that stays within a 5%(taxi) or 2%(race) deviation from the imaginary line is called the Minimum Linear Pulse Time (MLPT) and occurs at minimum duty. 2% is generally accepted as the correct deviation, while 5% tends to be a marketing angle to make the injectors look like they have a good range.

The ratio of the highest achievable flow (while constrained within the 5% or 2%) to the MLPT is called the Dynamic Flow Range (DFR). For instance at MLPT the flow might be 10cc/opening (short pulse) and the highest flow (long pulse) staying within the deviation constraints is 200 cc/opening, the ratio would be 200/10 = 20 = DFR

So having read all that, just remember to consider the MLPT when selecting an injector, otherwise you may have a difficult time with idle. If anything else don't stray below 1 millseconds minimum pulse to achieve minimum required fuel. There are plenty of sizing calculators on the web. The general method of sizing is to calculate the flow required at a user specified static fuel pressure, with the formula:

(hp x BSFC)÷(DC xN) lbs/hr

hp = engine horsepower

BSFC= brake specific fuel consumption (eg 0.55lbs/hp/hr for normally aspirated and 0.6 for turbocharged. High performance 0.47lbs/hp/hr nornally aspirated)

DC = max duty cycle:- nominally 0.8

N = number of cylinders

Multiply by 10.5 for cc/min

HP = 0.746kW

Goto Calculator

Changing Injectors

If you are contemplating changing the injectors with another size be aware and mindful of:

the injector spigot size:- e.g. you have a 10mm original and a 9.6mm replacement;

coil impedance:- e.g. 14 ohm original and 2 ohm replacement;

body and nozzle length:- they make look the same, but lengths do vary;

socket type:- will you have to change the plugs?

For the CB90 for instance the dark blue 195500-1300 injectors found on:

1986-87 Ford TX3 & Mazda 626 FEH 2.0 litre turbo;

1988-89 Mazda 323 B6E 1.6 litre turbo;

1992-94 Mercury Capri 6 1.6 litre turbo;

are the same physical dimensions as the 195500-1670 models and are a good replacement to get 300+cc/min for turbo application. The only problem may be achieving low enough cycling to get the idle speed down (see MLPT previous section). Ford Telstar 2.2 litre injectors are also an alternative = 195500-1280
Tested Resistence: 13.9 Ohms
Flow tested at 40 psi:
22.5lbs/hr - 80% duty cycle
27lbs/hr - wide open

The GTti's 195500-1610 injectors, bearing a different part number may also be found on some Ford Couriers = Mazda Bravo.

Some members recommend upgrading the Gtti engines to

Nippon Denso
365 cc/min (33.9 lbs/hr)
red/orange
2.9 ohms
73.0 hp each
255 kPa
Toyota 4AGZE

when increasing standard performance, Beware the change of impedance (not normally a big issue as a new ECU is generally required to maintain correct mixtures, if upgrading from standard)

Changing Fuel Pressure

The amount of fuel volume increase/decrease is a square root function of the change in pressure drop across the injector. For example if you increased the net fuel pressure across the injector from 300kPa to 600kPa you would get an increase of sqrt(600/300) = 41% or a multiplier of 1.41. Obviously moderate increases in fuel rail pressure have a fairly insignificant impact on fuel flow.

High Flowing

Changing or modifying an injector for a larger capacity, but same sized body. Fraught with danger as the fuel spray pattern is usually adversely affected.

Flowing Injectors

Term often used to indicate that the injectors have matching flows. This is determined during the testing and cleaning process. Flowing (testing) will also allow matching the ECU control process for each injector that may have different flow characteristics to the others in the engine.

Daihatsu Part Numbers

The following figures are generally derived from member input.

Engine NipponDenso

Part No

Flow Rate

cc/min

Nominal

Pressure kPa

Coil

Resistance (ohms)

Colour
GTti CB70/80 993cc 195500-1610 stamped 728 295

250 kPa. Fuel pump rated 80 litres/hour min.

12.8 Red
HC-E 1295cc 195500-2141 (195500-2140)

160

250 kPa

12.8

Green

HD-E 1589cc 195500-2040 stamped 027

190(184)

250 kPa

12.8

Grey

HE -E 1499cc 195500-3030 160 250 kPa

12.8

Blue

CB90 993cc 195500-1670 stamped 227 Same as Ford Laser ± 130 250 kPa 12.7 Green

Follow ups

SteveS1
Posted: Sat Oct 30, 2004 5:48 pm Post subject:

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In the process of swapping HD injectors (grey) into HC manifold, and I notice that they have the same electrical connection. so no need for cutting and swapping connectors. bit of good news for swapping HD into 1993 charades.

HD (grey) injectors are marked 195500 2040 (off import engine)
HC (green) injectors are marked 195500 2140 (off 1993 G200RS charade)

perhaps the HC injectors with the different connectors are the 195500 2141 as mentioned in FAQ, from the older charades?


3banger
Posted: Thu Apr 27, 2006 9:26 pm Post subject:

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Here are the Daihatsu factory specs

Specified resistance of all injector types should read between 11-17ohms

G200 HCE 160cc/min
G203 HEE 160cc/min
G201 HDEG 184cc/min

This is using the factory spec fuel pressure of 245-255kPa, energising injector for 60secs and measuring fuel dispersed from injector over that period.

Scribblings

nippodenso 195500 2040 928 18