# Number of diesel injections per revolution

A modern TDI using a piezoelectric injector may have up to as much as five injections per power stroke as far as I've read.

Given a four stroke, four cylinder TDI engine using injectors of that type, is it reasonable to assume that the engine may in total perform 100 diesel injections per second at 1,200 rpm?

1,200 rpm = 20 revolutions per second.

As the engine has 4 cylinders, it has a power stroke occurring on every crankshaft rotation, implying 20 power strokes per second.

With up to 5 injections (including pilot injection, main, post, etc), is it reasonable to assume a modern TDI can in total perform up to 100 diesel injections per second of operation at 1,200 rpm?

Edit

The engine in question has a total of four cylinders. So while we know that a typical four stroke engine (1 cyl) will fire every other rotation of crankshaft, the engine discussed will fire every half rotation as a whole. Please correct me if I'm wrong

• Four stroke engines fire cylinders every other revolution. – Moab Jul 14 '18 at 16:45
• As Moab, also stated as i"it takes two revolutions of the crank to complete the full four stroke cycle : induction, compression, ignition, exhaust... So, you need to think about how you adjust your maths. – Solar Mike Jul 14 '18 at 16:48
• @Moab Yes, I know - but my question took into account that the engine was also 4 cylinders. Please see updated question – Erik Jul 14 '18 at 22:50
• @SolarMike see updated question – Erik Jul 14 '18 at 22:50

To sort out the confusion here is my analysis:

``````(rpm/2) * (num of cylinders) / 60
``````

The rpm is divided by 2 as it is a 4-stroke engine, divide by 60 for power strokes per second.

This gives:

``````(1200/2) * 4 / 60 = 40 power strokes per second
``````

Now the power stroke may have multiple injection pulses so you can now adjust by multiplying by 2, 3, 4, 5 etc - BUT this may not be a constant over the time - ie it may vary per power-stroke per piston as the load on the engine changes...

• Exactly what I thought and asked for confirmation about. I mistakenly assumed the engine to fire as a whole per rotation, when in fact it fires every half rotation. So 20 rpm -> 40 power strokes per second as you also calculated. This means that the engine can potentially perform as much as 200 diesel injections per second at a given moment – Erik Jul 15 '18 at 8:53