General Engine Technology and Theory

All that has to do with the power train, gearbox, clutch, fuels and lubricants, etc. Generally the mechanical side of Formula One.
gruntguru
gruntguru
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Joined: Sat Feb 21, 2009 6:43 am

General Engine Technology and Theory

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amho wrote:
Sun Jul 15, 2018 12:18 pm
I wish there was a general engine topic where we could interchange our knowledge about engines.
Does any knows how engine load is calculated base on data from TPS، map and engine crank rev sensor? I want the equation which ECU use to calculate load?
Another question is that how automatic gearbox calculate road load?Does it use map sensor numbers or it uses the data of speed, road slope and car weight to find load? what about weight of passengers?
There is one now.
The term "engine load" has many interpretations, but in a tuning sense it is best defined as "engine output as a percentage of maximum output at the current engine speed".
There are very few vehicles where "load" is actually measured. That would require a torque sensor somewhere in the driveline. Load is usually inferred from either MAP or TPS. A knowledge of engine speed is also needed (see the load definition above.) The vehicle maker has full knowledge of the engine characteristics, so if the engine speed and the MAP (or TPS) are known, the load is easy to determine.

Same goes for auto trans. Even before computers were used to control them, they used engine speed and throttle position ("kickdown cable") or manifold vacuum to determine load.
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Greg Locock
Greg Locock
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Joined: Fri Jun 29, 2012 11:48 pm

Re: General Engine Technology and Theory

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Bear in mind the ECU also knows the acceleration of the engine. So the model is

engine output torque=IMEP torque(from the injector pulse width etc) - acceleration torque

I had a vague memory that some manufacturers use the variation in engine speed as the cylinder fires for some torque related measurement.

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amho
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Joined: Thu Apr 30, 2015 8:15 pm
Location: Iran

Re: General Engine Technology and Theory

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I could find these notes about engine load on the net, lets share it:
According to SAE International SAE J1979 / ISO 15031-5 (dated: 2014-08-11), calculated engine load is calculated by the following equation:

LOAD_PCT = [current airflow] / [(peak airflow at WOT@STP as a function of rpm) *
(BARO/29.92) * SQRT(298/(AAT+273))]
Where:

- STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg BARO,
- SQRT = square root
- WOT = wide open throttle
- AAT = Ambient Air Temperature (in °C)

Characteristics of LOAD_PCT are:

- Reaches 1.0 at WOT at any altitude, temperature or rpm for both naturally
aspirated and boosted engines.
- Indicates percent of peak available torque.
- Linearly correlated with engine vacuum
- Often used to schedule power enrichment.
- Compression ignition engines (diesels) shall support this PID using fuel
flow in place of airflow for the above calculations.
You've seen the above equation for calculated engine load. Below is the calculation for absolute engine load:

LOAD_ABS = [air mass (g / intake stroke)] / [1.184 (g / intake stroke) *
cylinder displacement in liters]

Derivation:

- air mass (g / intake stroke) = [total engine air mass (g/sec)] /
[rpm (revs/min)* (1 min / 60 sec) * (1/2 # of cylinders (strokes / rev)]

- LOAD_ABS = [air mass (g)/intake stroke] / [maximum air mass (g)/intake
stroke at WOT@STP at 100% volumetric efficiency] * 100%.

Where:

- STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg (101.3 kPa)
BARO
- WOT = wide open throttle

The quantity (maximum air mass (g)/intake stroke at WOT@STP at 100%
volumetric efficiency) is a constant for a given cylinder swept volume.
The constant is 1.184 (g/liter 3) * cylinder displacement (liter 3/intake
stroke) based on air density at STP.

Characteristics of LOAD_ABS are:

- Ranges from 0 to approximately 0.95 for naturally aspirated engines,
0 – 4 for boosted engines
- Linearly correlated with engine indicated and brake torque,
- Often used to schedule spark and EGR rates,
- Peak value of LOAD_ABS correlates with volumetric efficiency at WOT.
- Indicates the pumping efficiency of the engine for diagnostic purposes.
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roon
roon
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Joined: Sat Dec 17, 2016 6:04 pm

Re: General Engine Technology and Theory

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The current engines (F1) fire fuel in from the edge of the combustion chamber on the exhaust side. The combustion chamber is disc shaped, or roughly coin-shaped. Why is this superior to injecting from the center of the coin?

saviour stivala
saviour stivala
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Re: General Engine Technology and Theory

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roon wrote:
Mon Jul 30, 2018 8:34 pm
The current engines (F1) fire fuel in from the edge of the combustion chamber on the exhaust side. The combustion chamber is disc shaped, or roughly coin-shaped. Why is this superior to injecting from the center of the coin?
If the “use of TJI in f1” pushers known about the use of this “injection from the side” use in F1, they would have called their “pushed use of combustion system in F1” on-its-side-TJI. And to hell with its pre-combustion chamber and the direct injection rules.