CommonRail - High pressure electronic diesel injection

Technical papers:
Modelling pressure waves in the rail

Paper on the effect of timing and duration of main and pilot injection. Mainly conserning noise levels.

Modelling of a diesel engine common rail injection system

Achieving lower exhaust emissions and better performance in an HSDI diesel engine with multiple injections

Optimizing the multiple injection settings for a HSDI diesel engine


AFAIK there is no general aftermarket common rail diesel ECU available. This makes it impossible to use a common rail diesel in applications where the stock ECU does not work. One popular application can be marinisation of car engines. Another might be putting modern diesels in older cars. Or for tractors or gensets or whatever...

One critical thing would be timing for injection


A modern diesel does multiple injections each stroke. The pilot (and sometimes double-pilot) injectin is mainly for reducing noise at low revs. It also has a big effect on soot and NOx formation. At higher revs (>3000-4000) the pilot injection is not needed and only the main injection is needed. The post injection happens after the main injection, it also reduces emissions. I have not found any information on how it effects the torque or feul efficiency.

Hence, at times we will have up to 3, or even 4, injections per stroke. These events will probably overlap between cylinders in some rev ranges on engines with more than say 5-6 cylinders. This may be difficult to implement. The hardware might also be limiting (recharging injector outputs etc).

pilot injection

~ -40degrees (2-4mm^3) Timing not critical. Optimal timing is dependant on load and revs.

Main injection

no load -2 - 4

part load -6 - 4

full load -15 - -6

duration 40-60 deg crank

5000 crank rpm = 5000 / 60 rps = 5000/60 * 360 degps = 33us/deg

average unexpected delay = 7us = 7/33 deg = 0.21deg

We need data on injector properties (reaction time and dwell time as well as electrical properties.)

We also need to know how critical the timing is. Is it the timing resolution or stroke-to-stroke repeatability that is important?

Required I/O:

Glow plug output.

A small typical diesel like Volvo D5244T4-7 uses max 12V and 22A during a minute. Most engines has a separate relay for this. Some engines regulate the voltage (and hence current) over the glow plug. The purpose is to reach high temperatures fast with a high current, after which the current is lowered to maintain the temperature. On larger (more plugs) or older engines it might not be feasable to output the required current directly from the ECU. It might then be better to control a relay.

Rail pressure sensor input

Commonly outputs 0-5V. Needs +5V and an ADC

Rail pressure control valve output

PWM regulated electromagnetic valve with coil resistance of 2-3Ohms.

Unit injector

PWM regulated (pull and hold) up to 20A@80V for an typical electromagnetic injector. I don't have any data for piezolectric ones.

Commanded throttle position

0-5V or CAN

Manifold Air Pressure (MAP)

Manifold Air Temperature

Oil pressure

Coolant temperature

Crank shaft rotation sensor

Cam sensor

I/O for variable geometry turbo control


I/O for swirl throttle, output to pull starter selenoid.

Any comments would be greatly appriciated. I am also very intrested in pointers to information on diesel injection, injectors, workshop manuals and almost everything else concerning common rail diesels.

Here is a basic diagram for I/O (Performance application) needed for a Diesel ECU. I can try to find the injector times, but I wouldn't worry about it, as different makers will have different timings. It will have to be a varable in the ECU that gets added to the Injection event timing.

Also found that time between mutliple injections is ~ <=200usec, this may be lower with piezo, I will keep looking.