BMW-335i (E90 N54)

[Richard L]

Forwords for the N54 application


The N54 engine
... is blessed with a vey intelligent engine management system.
One of the many great features is very beneficial to water/methanol injection.

Some basics:
- The engine management (DME) is only as intelligent as what it can process from multiple sensors.
- The power output from a given condition is limited by quality rather than quantity of fuel ingested.

Water/methanol injection:
The main function is to provide inlet, in-cylinder cooling and some octane enhancement.
When the DME is seeing cooler charge air and absence of knock, it will not limit power to protect the engine.

How much is too much?
The limit will depend on the DME?s ability to pull fuel to maintain correct air-fuel ratio.
The N54 engine is equipped with two lambda sensor to monitor each bank of three cylinders.
Unfortunately it cannot read each cylinder individually so lambda (excess oxygen) is
based on the weakest cylinder, other cylinders will be running rich especially a large amount of
water/methanol is injected in the inlet tract without any guarantee of even distribution.

A few solutions?
1. Avoid injecting high ratio of methanol to fuel so the afr variations between cylinders are minimised.

2. Port injection is one way to overcome this variation. There is cost consideration as well as the
risk of one clogged jet. A good failsafe is therefore essential. Although the DME can replace the
lean cylinder but also means the other two cylinders will be running pig rich until the clogged jet is serviced.

3. Placing the jets as far away from the throttle is one way to improve the cylinder distribution.
Longer inlet path allows more evaporation to take place and better cooling. Reduction of droplet
size (mass) by the process of evaporation promotes even cylinder distribution.

4. A delivery system that will keep the methanol ratio constant so the DME can pull fuel gently
rather abruptly. A single stage based at one trigger point is not ideal unless you live life
by the quarter mile or only interested in WOT dyno results.

In conclusion...
if you are investing on a wmi system, why compromised for the sake of a
hundred dollars or two on a system that will perform well under all load
condition with a proper failsafe. You will only get what you paid for.