Honda Power Unit Hardware & Software

[Tommy Cookers]

~14 degrees after TDC is where the rod and piston assembly can transfer maximum mechanical leverage to the crank, thus it is the ideal point to have highest cylinder pressure.
This will vary slightly with deck height and rod ratio.

around 14 deg atdc the 'leverage' is very small - (the formal term for leverage is mechanical advantage)
this MA (ie the ratio of gas force to crankshaft force) is largest around midstroke
(but of course the gas force has fallen by this point)

the engine works (converts pressure work to mechanical work) by expansion of hot gas against a load
(work is gas force multiplied by piston travel - there is no work done without piston movement)
this expansion is usefully large when the piston goes from near tdc towards midstroke

it's a compromise
this is an efficiency formula not a 'power' formula
and the compromise will also be different with the high exhaust pressure and turbine power recovery

regarding rod ratio ....
the lowish rpm suggests (unlike NA F1) that a conservative ie 'long' RR is not necessary
but also that a short RR is not necessary
isn't RR rather fixed by the ICE dimension rules ?

[godlameroso]

RR doesn't affect displacement, only deck height, thrust loads on the piston skirt, as well as affecting dwell times @ TDC and BDC, which is related to momentum change of the piston.

[dren]

regarding rod ratio ....
the lowish rpm suggests (unlike NA F1) that a conservative ie 'long' RR is not necessary
but also that a short RR is not necessary
isn't RR rather fixed by the ICE dimension rules ?

There's a height lower limit in reference to the reference plane for the crank journal bearings. The cylinder volume, spacing, angle and bore sizing is set. CR has a max a max cap of 18:1. So, the rest can be varied to some degree.

[saviour stivala]

Bore size is fixed by the rules and that automatically fixes bore/stroke ratio. crankshaft center height as well as bearing sizes are also fixed by rules. con-rod length (center to center) to crank radius ratio is free from rules. 14 degrees ATDC is recognized by engine experts as the best point for PCP/PPP to occurs, this point applies the greatest burn pressure force on the crankshaft at the optimum crankshaft angle and will result in the maximum possible power stroke duration. When the engine achieves PCP/PPP at 14 degrees ATDC then maximum brake torque (MBT) is produced. shift the PCP/PPP position and less MBT is produced.The faster the engine is rotating, the shorter the time for the crankshaft angle to reach PCP/PPP. Ignition is set at maximum MBT produced and retarded at the knock limit.

[Tommy Cookers]

RR doesn't affect displacement, only deck height, thrust loads on the piston skirt, as well as affecting dwell times @ TDC and BDC, which is related to momentum change of the piston.

did anyone say that RR affects displacement ?
low RR increases all lateral components of piston load
ie inertial-related and compression-related loads as well as (power) 'thrust'-related loads
remember the compression work is unusually high in these engines
and eg the inertia-related lateral loads were in the NA F1 the biggest part of piston frictional power loss

what's momentum got to do with anything ?
RR determines piston motion ie a short rod produces higher peak piston accelerations and stress

[gruntguru]

In my opinion rapid or slow combustion does not change the need for ATDC optimum (PCP - PPP) point (greatest possible burn pressure force on crankshaft angle and for maximum possible power stroke duration). what will need change will be the ignition point (ignition point advance). when the engine achieves (PCP - PPP) at 14 degrees ATDC then maximum brake torque (MBT) is produced, shift the (PCP -PPP) position and less (MBT) is produced. the faster the engine is rotating, the shorter the time for crankshaft angle to reach (PCPN - PPP).

You might have missed the point. 14* is not a magic number. Different engine designs will result in a different value for the optimum value for PCP.

With the rapid combustion obtained with TJI it is likely that PCP for the F1 engines occurs at less than 14*.

I did not miss your point and I did not call the 14 degree ATDC a magic number. Agree that different engine designs could result in a different value for the optimum PCP/PPP + MBT, but any number above that will come at the cost of a shorter power stroke duration. But I do not agree that a rapid or slower burn will move or effect the moving of the 14 degree ATDC optimum point. The engine designs items that can move that optimum point is as Godlameroso has explained (con-rod center to center length to crank radius ratio). The 14 degree ATDC number seems to me to be the number vastly agreed upon by most people that matter, some people also that matter, sometimes adds (+) 1 to 2 degrees to the number 14 for some con-rod length/crank radius ratios but admits that will result in a shorter power stroke duration. Also I never read anybody deducting (-) any degrees from the number 14.

The number 14 means nothing. Leaving aside detonation and pressure rise rate (which must be limited for mechanical reasons - typically to less than 10 bar/degree), ignition timing will be set at the value which produces best torque at the given operating point (MBT). This will result in the pressure peak occurring at some point ATDC.

Lets take an extreme case. An engine has extremely rapid combustion (again at some particular operating speed and load). The entire burn takes only 10* of crankshaft rotation. If the pressure peak is to occur at 14* ATDC, the spark timing (ignoring ignition delay) will need to be set at about 9* ATDC. This is ridiculous because the optimum spark timing in this case would be very close to TDC and the pressure peak would be at about 5* ATDC.

"Agreed apon by most people that matter" Well now you must be talking about "performance engine tuners" and such rules of thumb (magic numbers) only apply to the engines that we are all familiar with and constitute 99% of the work that this group do.

The first image below gives some idea of the different burn rates for conventional ignition vs TJI. All these data points are for optimised timing (MBT). If you look at the right-hand red dots you can see at lambda 1.4, the conventional system fires the spark at 40* BTDC, 10% of the fuel mass has burned by 5* BTDC, 50% by 5* ATDC and 90% by 25* ATDC. Peak pressure would occur somewhere between the last two numbers (5* - 25* ATDC) so perhaps close to 14* ATDC. At the same AFR the light green TJI angles are 20* BTDC, 1* BTDC, 7* ATDC and 18* ATDC. Peak pressure at perhaps 12* ATDC.

Notice the 50% burn angle (a number often quoted by researchers and called "CA50") ends up being very similar (about 7* ATDC) at different AFRs, ignition systems and burn rates. Likewise CA50 stays about the same for different engine speeds (bottom image). CA50 is clearly a preferred metric for "people who really know" and is obviously one that is more reliable than PCP as a predictor of MBT.

@SS and @godlameroso.
Any talk of "cylinder pressure occurring at optimum crank angle/geometry/mechanical advantage" is rubbish. Work done during the power stroke is the integral of PdV. It doesn't matter what the mechanism below the piston does. If a more favourable mechanical advantage is able to extract more work early in the stroke, there will be less work extracted later in the stroke - period!





CITATION: Attard, W. and Blaxill, H., "A Gasoline Fueled Pre-Chamber Jet Ignition Combustion System at Unthrottled
Conditions," SAE Int. J. Engines 5(2):2012, doi:10.4271/2012-01-0386.

[saviour stivala]

When the engine produces PCP/PPP at 14 degrees ATDC it is producing and applying the greatest burn pressure force on the crankshaft at the optimum crankshaft angle and that will result in maximum possible power stroke duration. When PCP/PPP is achieved at 14 degrees ATDC the maximum MBT is produced. Shift the PCP/PPP position and less MBT is the result. Ignition point is set at maximum MBT produced and retarded at knock limit regardless of what is being burned and regardless of rapid, slower burn stuff or shape, style, type of chamber and combustion in use.

[godlameroso]

The graph shows ~90% burn rate at ~14° ATDC for both gasoline and TJI, only varying due to air concentration in the mixture. Which is expected gasoline engines like to run a little rich ~.7-.9 lambda.

On mechanical advantage, think of a swing, there's a specific moment in the swing where someone pushing you will will add the most momentum(especially important if you want to get really high and impress all the playground girls.) This moment is just as the swing is going away from you(the person pushing).

Likewise each combustion event is a push on the piston, you do not want the push to come on half way through the power stroke where piston speed is already greatest, and where CC volume is high, and compression ratio is low. You want the push to come when piston speed is low relative to other parts of the stroke. Ie at the start of the down swing.

After and before TDC the piston has what's called dwell time, during dwell time the piston moves very slowly relative to the middle of it's travel.

~14° ATDC is the best compromise between compression ratio, expansion volume, piston speed, and piston momentum, thus the ideal place to give a piston a push(especially important if you're trying to impress the girls at the race track).

[HPD]

Verstappen: "In racing simulator I tried the first tests for 2019. From Honda we get all the data.The engines run on the test benches, which we can connect to the simulator at Red Bull Racing.

The change has the most impact on the transmission, in terms of the changed load. The cooling must also be kept upside down. But we have the right people and the know-how to tackle everything. It looks good,"

[saviour stivala]

The graph shows ~90% burn rate at ~14° ATDC for both gasoline and TJI, only varying due to air concentration in the mixture. Which is expected gasoline engines like to run a little rich ~.7-.9 lambda.

On mechanical advantage, think of a swing, there's a specific moment in the swing where someone pushing you will will add the most momentum(especially important if you want to get really high and impress all the playground girls.) This moment is just as the swing is going away from you(the person pushing).

Likewise each combustion event is a push on the piston, you do not want the push to come on half way through the power stroke where piston speed is already greatest, and where CC volume and compression ratio is low. You want the push to come when piston speed is low relative to other parts of the stroke. Ie at the start of the down swing.

After and before TDC the piston has what's called dwell time, during dwell time the piston moves very slowly relative to the middle of it's travel.

~14° ATDC is the best compromise between compression ratio, expansion volume, piston speed, and piston momentum, thus the ideal place to give a piston a push(especially important if you're trying to impress the girls at the race track).

The swing-aid-push (best point to push) is an excellent explanation PROSIT.

[godlameroso]

On another note a very interesting bit of data from the graph shows jet ignition works better with better fuel vaporization, which is consistent with common sense and other studies. I wonder how much gains have come from further vaporizing fuel past the 500 bar injection limit. Using fuel heaters, acoustics, etc to aid atomization.

On another semi-related note, if rod ratio has any appreciable effect in this engine formula it's for engine harmonics and reducing friction more than anything else.

[saviour stivala]

Formula 1 engines has always used/favored higher rod length to crank radius ratio, always used a ratio higher than 2.0:1 as opposed to what seems the preferred lower than 2.0:1 used for fast road engines.
The 18000RPM NA 2.4L V8 using a bore/stroke ratio of 2.46:1 were using a rod ratio of 2.56:1.
Longer rods with same stroke improves combustion efficiency and squeezes a little more power from mid-range to peak RPM. Also will reduce cylinder side forces, reduce the level of vibration inside engine, reduce coolant and oil temperatures. A longer rod makes more torque with same piston force and decreases friction.

[Tommy Cookers]

didn't the NA engine freeze (just where MB/Ilmor had reached) in effect freeze the RR at a conservative value ?
the high RR (for a given rpm) gives less piston acceleration and so less stress and longer engine life
the low RR gives a lighter lower engine and so better aero

before special fast-burning fuels that made very high rpm worthwhile some top F1 engines mep was improved by low RRs
low RR (not high RR) alleviating combustion speed/consistency issues
though ring behaviour eg flutter may be critically affected by piston acceleration and so discourage low RRs
Peugeot V10s once used a ring that fluttered below race rpm but the driver Mr Brundle said he wasn't told (it blew on the grid)

isn't RR rather insignificant to F1 now ?
GG's plots from the Attard book seem to show that combustion speed with such leaning (or vice-versa) is important

[gruntguru]

When the engine produces PCP/PPP at 14 degrees ATDC it is producing and applying the greatest burn pressure force on the crankshaft at the optimum crankshaft angle and that will result in maximum possible power stroke duration. When PCP/PPP is achieved at 14 degrees ATDC the maximum MBT is produced. Shift the PCP/PPP position and less MBT is the result. Ignition point is set at maximum MBT produced and retarded at knock limit regardless of what is being burned and regardless of rapid, slower burn stuff or shape, style, type of chamber and combustion in use.

This is nonsense. Best output and efficiency would occur if all the charge was burned at TDC and then expanded for the entire power stroke. In this (idealised, unrealistic) scenario, PCP occurs at TDC.

14* might be a good number for the majority of engines but the new fast-burn technologies are allowing this number to be reduced with corresponding increases in efficiency.

"Based on test data, it has been found that the peak cylinder pressure usually occurs around 15* ATDC at MBT timing. The 50% mass fraction burned point generally occurs from 8* to 10* ATDC when MBT timing is achieved, see [4]. The algorithm published in [3] controls PR(10) (normalized pressure ratio of incylinder and motoring pressure at 10* ATDC) around 0.55 to obtain the MBT timing. Because these criteria are solely based upon observations and may change at different operating conditions, each algorithm still requires some calibration effort. It is clear that the combustion process has to be matched with the engine cylinder volume change to attain the best torque. However, there is no sound theory to support the rationale that peak cylinder pressure must occur around 15* ATDC or that 50% burned must happen around 9* ATDC for the MBT timing conditions."

Zhu, G.G., Daniels, C.F., & Winkelman, J. (2004). MBT Timing Detection and its Closed-Loop Control Using In-Cylinder Ionization Signal.

[gruntguru]

On another note a very interesting bit of data from the graph shows jet ignition works better with better fuel vaporization, which is consistent with common sense and other studies. I wonder how much gains have come from further vaporizing fuel past the 500 bar injection limit. Using fuel heaters, acoustics, etc to aid atomization.

I should point out that the graph is referring to atomisation in the pre-chamber only.