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Self-Study Programme 02

Open ECU

Design and Function

How an engine control unit knows where the engine is, decides when to inject and ignite, and how an Open ECU puts those decisions in the researcher's hands.

Start reading

Applies to: R&DU04, R&DU13, R&DU15, R&DU01, and all -OECU engine rigs (13). Read SSP 01 first if you are new to engine test rigs.

Chapter 1

Why an Open ECU

Every modern engine is run by an electronic control unit (ECU). It reads sensors, looks up the right injection and ignition settings in stored maps, and drives the injectors and ignition. In a production engine those maps are fixed by the manufacturer and locked.

Production ECU

  • Injection timing, quantity and pressure come from fixed maps
  • Maps are locked and cannot be read or changed
  • Optimised for one engine, one fuel, one emissions standard

Open ECU

  • You set injection timing, duration, pressure and spark timing yourself
  • Change one parameter at a time and see its effect on combustion
  • Run alternative fuels and injection strategies the production map was never built for

Chapter 2

Sensors and actuators

The ECU sits between sensors that tell it what the engine is doing and actuators that act on the engine. Choose a kit to see its components.

SensorsControl unitActuators Crankshaft positionvariable reluctance Camshaft positionHall effect Mass air flow (MAF)hot wire T-MAP (pressure + temp)NTC Rail pressure Open ECUInfineon processoryour maps and set-points Diesel solenoid injector High-pressure pump (Bosch CP-1) Petrol direct injector Port fuel injector (2.8 bar) Gas injector Ignition coil / spark EGR valve PC: CAN + K-line calibration
Crankshaft position sensor
A variable-reluctance sensor facing a toothed crank trigger wheel. Each tooth gives a pulse; the ECU counts them to know crank angle and speed.
Camshaft position sensor
A Hall-effect sensor on a cam trigger wheel. The camshaft turns once per four-stroke cycle, so it tells the ECU which revolution is the firing one.
MAF and T-MAP sensors
Hot-wire mass air flow, and manifold absolute pressure with an NTC temperature sensor: together they tell the ECU how much air the engine is taking in.
Rail pressure sensor
On CRDI and GDI kits: measures fuel pressure in the common rail. On the CRDI kit the ECU uses it to hold rail pressure at your set-point (closed loop).
Injectors
Solenoid injectors open for as long as the ECU energises them. Opening time and fuel pressure together set the quantity injected.
EGR valve
Lets a controlled flow of exhaust gas back into the intake (chapter 6).
CAN and K-line
The links between the ECU and your PC for changing settings, monitoring live values and troubleshooting.

Chapter 3

Where is the crankshaft?

Before the ECU can inject at "10° before TDC" it must know the crank position to within a degree. A four-stroke cycle takes two crank revolutions (720°), so it needs two signals. Move the slider through one complete cycle.

Crank signal

One pulse per tooth. A gap where teeth are missing (for example a 36-1 wheel) marks a known position once every revolution; counting teeth from the gap gives the angle.

Cam signal

One pulse per cycle. The crank signal looks the same on both revolutions — the cam pulse tells the ECU whether the next TDC is compression (firing) or exhaust.

Together

Gap + tooth count + cam phase = absolute position in the 720° cycle. The ECU can then schedule injection and spark to the degree.

Tooth count shown is a typical example; check your kit's trigger wheel.

Chapter 4

What you can tune

Each kit exposes the settings that matter for its injection system. Angles are measured in crank degrees before (bTDC) or after the firing top dead centre. Choose a kit and move the settings.

CRDI (R&DU04)

Pilot and main start angles, main duration in crank degrees, closed-loop rail pressure 200–1100 bar, EGR flow and closed-loop idle speed.

GDI (R&DU13)

Start of injection for homogeneous operation, end of injection for stratified operation, spark timing, open-loop rail pressure 10–110 bar; the ECU calculates the duration.

PFI (R&DU15)

End angle of injection and spark timing at 2.8 bar injection pressure; the ECU calculates the duration.

Gas (R&DU01)

Injection start angle and injection duration for gas injected into the intake manifold, open loop.

Chapter 5

Injection quantity

The fuel delivered per stroke depends on how long the injector is open and on the pressure pushing fuel through the nozzle holes. Duration is set in crank degrees, so it gets shorter in time as speed rises: t = CA° ÷ (6 × N).

Try your own settings

Opening time

t = CA° ÷ (6 × N)

1.20 ms

Jet velocity

v = √(2 ΔP / ρ), ΔP = rail − cylinder

425 m/s

Fuel per stroke

Q = Cd × Aholes × v × t = 24.2 mm³

20.1 mg

Chapter 6

Exhaust gas recirculation

What it does

The EGR valve lets some exhaust gas back into the intake. Exhaust gas is mostly inert (CO₂, H₂O, N₂), so it dilutes the fresh charge and absorbs heat. Peak flame temperature falls — and with it the formation of nitrogen oxides (NOx).

The trade-off

Too much EGR leaves too little oxygen: combustion slows, smoke and unburnt fuel rise and efficiency drops. Finding the best EGR rate at each load is a typical Open ECU experiment.

Measuring the EGR rate

The usual method compares CO₂ in the intake (after mixing) with CO₂ in the exhaust: EGR % = (CO₂ intake − CO₂ ambient) ÷ (CO₂ exhaust − CO₂ ambient) × 100.

EGR rate

Example: intake 1.8 %, exhaust 9.0 % CO₂

19.6 %

Chapter 7

Calibrating safely

An Open ECU removes the limits a production map builds in. Work methodically:

  1. Start from the baseline

    Load the supplied baseline settings and record a reference test at each load point before changing anything.

  2. Change one parameter at a time

    For example move main injection 2° earlier, keep everything else fixed, and record performance and combustion data.

  3. Watch the limits

    Peak cylinder pressure, rate of pressure rise, exhaust temperature, knock (petrol) and smoke. Stop and step back if any approaches the engine's limit.

  4. Let it settle

    Wait for steady temperatures before logging each point, as in SSP 01.

  5. Record your settings with the data

    Note every set-point (timing, duration, pressure, EGR) with each result file, so the test can be repeated.

  6. Return to baseline

    Restore the baseline settings at the end of the session and before handing the engine to the next user.

Chapter 8

Test your knowledge

  1. Why can't a production ECU simply be used for engine research?

  2. Which signal tells the ECU exactly where the crankshaft is?

  3. Why does the ECU also need a camshaft position signal?

  4. On the CRDI kit, rail pressure is adjustable between…

  5. What is the purpose of a pilot injection in a diesel engine?

  6. On the GDI kit, stratified operation is set by…

  7. A port fuel injection (PFI) system injects fuel…

  8. Injection duration set as 12 crank-angle degrees at 1500 rpm lasts…

  9. Raising rail pressure with the same injection duration…

  10. Exhaust gas recirculation (EGR) is mainly used to…

Answers

  1. Its injection and ignition settings come from fixed, preprogrammed maps
  2. Crankshaft position sensor on the crank trigger wheel
  3. To tell the compression stroke from the exhaust stroke, since the crank turns twice per cycle
  4. 200 and 1100 bar
  5. To start combustion gently before the main injection, reducing the pressure rise rate and noise
  6. The end of injection, late in the compression stroke
  7. Into the intake port, at about 2.8 bar on this kit
  8. 1.33 ms
  9. Injects more fuel, with finer atomisation
  10. Lower combustion temperature and so reduce NOx

The Open ECU kits