SFOC Ambient Correction: Air and Cooling Water Temperature

Formula, assumptions, and limits

Adding the Table 2.05.02 factors, a MAN B&W two-stroke burns 1.06% more fuel per kWh at the tropical design condition of 45 °C air and 36 °C cooling water than at the ISO reference with Pmax adjusted, and 1.87% more without. The table is in the Everllence (formerly MAN Energy Solutions) B&W G60ME-C10.5 project guide, July 2026, section 2.05, headed “All Engines” and dated 2026-06-01.

Formula

For a two-stroke, corrected SFOC equals ISO SFOC multiplied by one plus a sum of percentages: for each condition, its Table 2.05.02 factor times its deviation from the reference in steps of 10 °C or 10 mbar.

• $T_{air}$: blower (turbocharger) inlet air temperature, °C, reference 25 °C.
• $T_{cw}$: scavenge-air cooling water inlet temperature, °C, reference 25 °C.
• $p$: blower inlet barometric pressure, mbar, reference 1,000 mbar.
• $c_{air}$, $c_{cw}$, $c_{p}$: the Table 2.05.02 factors below, in percent per 10 °C or per 10 mbar.

For a MAN single-stage turbocharged four-stroke, the L23/30DF project guide, section B 11 01 0, multiplies reference SFOC by a factor β. β adds 0.06% per °C of site air above the reference, 0.04% per °C of charge air above the engine type’s reference, and 7% per bar of pressure below the reference (temperatures in °C, pressures in bar):

Here $t_x$ is the site air temperature, $t_{bax}$ the charge air temperature before the cylinder, $t_{bar}$ the engine type’s reference charge air temperature, and $p_x$ the site pressure. MAN’s own example takes $t_r$ = 25 °C and $p_r$ = 1.0 bar.

Derivation

ISO 3046-1:2002 adopts the ISO 15550:2002 reference state (clause 5): 100 kPa, 25 °C air, 30% relative humidity and 25 °C charge-air coolant. Its power adjustment (eqs. 1 to 3, ratio k with exponents m, n and s) takes the exponents from Table 2, and the row for low-speed two-strokes reads “nr”: no values are recommended and the engine maker uses its own. MAN publishes its own as the percent factors above. MAN’s four-stroke β is MAN’s own linear method, which the guide says it specifies “in accordance to ISO 3046-1:2002”.

The cooling water term acts through the scavenge air. The guide’s footnote says a 1 °C rise in cooling water raises scavenge air temperature by 1 °C and, “if Pmax is unchanged”, SFOC by 0.06%. That rate matches the Pmax-adjusted column (0.60% per 10 °C), not the not-adjusted one (0.41%); the calculator uses the table.

Assumptions

• The three two-stroke terms add. MAN gives each factor on its own and states no rule for combining them; adding is the calculator’s choice.
• The factors are linear across the entered range.
• The factors are applied unchanged at every engine load; MAN gives them with no load dependence.
• The fuel is at the reference LCV of 42,700 kJ/kg, or the input SFOC is already converted to it.
• The input SFOC is at ISO conditions, not an as-measured sea figure.

Worked example

A two-stroke rated 165 g/kWh at ISO runs at 45 °C blower inlet air and 36 °C cooling water, 1,000 mbar:

The four-stroke check is MAN’s own example: 200 g/kWh at 45 °C air, 50 °C charge air against a 40 °C reference and 0.9 bar gives β = 1 + 0.012 + 0.004 + 0.007 = 1.023, so 204.6 g/kWh.

Edge cases and limits

• MAN’s CEAS tool accepts 10 to 45 °C air and 10 to 36 °C cooling water (paper 5510-0074-03). MAN states no range for the Table 2.05.02 factors themselves; outside the CEAS band the calculator still applies them and shows a note.
• The four-stroke formula is stated for 5 to 55 °C air, 25 to 75 °C charge air and 0.885 to 1.030 bar. Outside it the calculator doesn’t return a figure.
• No SFOC factor for exhaust back pressure is published in Table 2.05.02; MAN gives back pressure only against exhaust temperature and amount.
• Humidity isn’t a term in the two-stroke table.
• The four-stroke formula is stated “for 1-stage turbocharged engines”; section B 11 01 0 lists the L28/32H, L27/38, L23/30H, L21/31 and L16/24 with their S variants, and the V28/32S.
• The guide’s SFOC guarantee tolerance of 5% at 100% SMCR is separate from this correction.

Regulatory basis

The EEDI takes SFC corrected to the ISO reference, the reverse of the direction this calculator runs. MEPC.364(79), as amended by MEPC.410(84), paragraph 2.2.7.1:

The SFC should be corrected to the value corresponding to the ISO standard reference conditions using the standard lower calorific value of the fuel oil (42,700kJ/kg), referring to ISO 15550:2002 and ISO 3046-1:2002.

MEPC.411(84), the 2026 EEDI survey and certification guidelines adopted on 1 May 2026 to supersede MEPC.365(79), adds in paragraph 4.2.4 that the approved NOx Technical File and a documented summary of the correction calculations go to the verifier.

Common errors

1. Seawater entered as cooling water. Table 2.05.02 means the water at the scavenge air cooler inlet. On a central cooling system controlled to MAN’s options A or B it runs about 4 °C above seawater (36 °C against 32 °C sea at the tropical design point); on a plant held at a fixed 36 °C set point it stays at 36 °C. Enter the measured inlet temperature.
2. Deck temperature entered as blower inlet. With an engine-room intake, MAN puts the air about 4 °C above the outside deck temperature.
3. Correcting a sea figure. Applying the factors to a sea-trial or noon-report SFOC that already reflects site conditions counts the ambient effect twice.
4. Using the two-stroke factors on a WinGD engine. WinGD publishes no numeric correction in its X72-B installation manual; its GTD tool is the source for those engines.

How to use this calculator

1. Select the engine type: MAN B&W two-stroke, or MAN single-stage turbocharged four-stroke.
2. Enter the SFOC at ISO reference conditions from the shop test or the project guide.
3. Enter the site conditions: blower inlet air temperature and barometric pressure, plus the cooling water temperature for a two-stroke, or the charge air temperature and its reference for a four-stroke. The “Load MAN’s worked example” button fills the four-stroke inputs from the guide.
4. For a two-stroke, choose whether Pmax is adjusted. The line under the corrected SFOC shows the other column.
5. Read the corrected SFOC and the table that splits the correction by condition.

Cooling water vs intake air: which raises SFOC more

On a MAN B&W two-stroke, scavenge-air cooling water raises SFOC more than intake air when Pmax is adjusted, and intake air raises it more when Pmax is left alone. Table 2.05.02 of the G60ME-C10.5 project guide gives 0.60% per 10 °C of cooling water against 0.20% for blower inlet air with Pmax adjusted, or 0.099 against 0.033 g/kWh per °C at 165 g/kWh. Without adjustment the order flips: 0.71% for air against 0.41% for cooling water.

MAN’s 2023 paper puts the cooling water effect at about 1.0 g/kWh per 10 °C, and 2.5 g/kWh for 36 °C cooling water against 10 °C. That matches the adjusted column (0.60% of 165 g/kWh is 0.99 g/kWh per 10 °C), which is why the calculator opens on it.

A ship moving from the North Sea to the Arabian Gulf gains both temperatures at once. The calculator’s breakdown table shows how much of the change each one carries, which is the number to check before blaming the hull or the fuel for a rise in daily consumption.

Where to find each input

SFOC at ISO comes from the engine’s shop test report or MAN project guide, and the two temperatures come from the engine monitoring system, not the bridge or deck readings.

• SFOC at ISO: the shop test report or the engine’s project guide SFOC curve, both stated at the ISO reference and 42,700 kJ/kg.
• Blower inlet air temperature: the turbocharger inlet sensor on the engine’s monitoring system, not the bridge or deck reading.
• Scavenge-air cooling water inlet: the LT cooling water temperature at the scavenge air cooler inlet. MAN recommends controlling it to a 10 °C set point, or to 4 °C above seawater (paper 5510-0074-03).
• Barometric pressure: the engine-room or bridge barometer, in mbar.
• Four-stroke reference charge air temperature: the engine type’s value in the SFOC section of its MAN project guide.

Related calculators

Converting a corrected SFOC into brake thermal efficiency is the job of the engine thermal efficiency calculator. The EEDI attained calculator takes SFOC at the ISO reference, the figure this page converts from. The cooling water factor assumes the guide’s 1 °C for 1 °C link between cooling water and scavenge air; a fouled cooler breaks that link, and the charge air cooler effectiveness calculator measures by how much.

The CII SFOC and fuel mix quick check takes a main-engine SFOC as its input; feed it the site-corrected figure when the ship trades far from the ISO reference. The scavenge air pressure calculator estimates two-stroke scavenge pressure from the turbocharger pressure ratio and ambient conditions, the same blower inlet state this page corrects SFOC for.

Further reading

• Specific fuel oil consumption
• SFOC curves
• Marine diesel engine
• Slow steaming and engine cleanliness

Test cases this calculator passes

Every build of this site runs these cases through the calculator above and stops the release if any figure moves outside its tolerance. Load a case to put its inputs into the calculator.

Frequently asked questions

How much does SFOC rise per °C of intake air temperature?

On a MAN B&W two-stroke, Table 2.05.02 of the Everllence G60ME-C10.5 project guide gives +0.20% of SFOC per 10 °C rise in blower inlet temperature with Pmax adjusted, and +0.71% per 10 °C without. At 165 g/kWh that is about 0.03 and 0.12 g/kWh per °C. MAN's four-stroke β formula uses 0.06% per °C of ambient air.

Does seawater temperature affect SFOC more than air temperature?

With Pmax adjusted, yes. The same MAN table gives +0.60% per 10 °C of scavenge-air cooling water against +0.20% for blower inlet air. Without Pmax adjustment the order flips: +0.71% for air against +0.41% for cooling water. The cooling water is usually central fresh water: about 4 °C above seawater on MAN's control options A and B, or held at 36 °C where the yard specifies a fixed set point.

What are the ISO reference conditions for SFOC?

ISO 3046-1:2002 and ISO 15550 set 100 kPa (1,000 mbar), 25 °C air, 30% relative humidity and 25 °C charge-air coolant. MAN B&W states its two-stroke SFOC at 1,000 mbar, 25 °C air and 25 °C scavenge-air cooling water, with a fuel lower calorific value of 42,700 kJ/kg.

How is shop-test SFOC corrected for the EEDI?

MEPC.364(79), as amended by MEPC.410(84), paragraph 2.2.7.1 states that the SFC from the NOx Technical File test report should be corrected to the ISO reference conditions at an LCV of 42,700 kJ/kg, referring to ISO 15550:2002 and ISO 3046-1:2002. MEPC.411(84), the 2026 EEDI survey and certification guidelines that superseded MEPC.365(79), asks in paragraph 4.2.4 for a documented summary of the correction calculations to go to the verifier.

Do these factors apply to WinGD engines?

Not on any published basis. WinGD's X72-B Marine Installation Manual (2023) states the same 25 °C reference but publishes no numeric fuel correction, routing non-ISO performance through its GTD tool. ISO 3046-1:2002 Table 2 recommends no exponents for low-speed two-strokes.

What does Pmax adjusted mean in the MAN SFOC correction?

Pmax is the engine's maximum cylinder firing pressure. MAN B&W Table 2.05.02 gives one column with Pmax adjusted at the site condition and one without. Hotter blower inlet air costs 0.20% of SFOC per 10 °C with Pmax adjusted and 0.71% without, so adjustment recovers most of the air-temperature penalty. For cooling water the order reverses: 0.60% adjusted against 0.41% not adjusted.

How much more fuel does a two-stroke burn in tropical conditions?

At MAN's tropical design point of 45 °C blower inlet air and 36 °C scavenge-air cooling water, with seawater at 32 °C, Table 2.05.02 puts a MAN B&W two-stroke 1.06% above its ISO SFOC with Pmax adjusted and 1.87% above without. At 165 g/kWh that is 166.7 and 168.1 g/kWh.

What cooling water temperature gives the lowest SFOC?

The colder the water at the scavenge air cooler inlet, the colder the scavenge air and the lower the SFOC. MAN's 2023 paper 5510-0074-03 puts the effect at about 1.0 g/kWh per 10 °C, and 2.5 g/kWh for 36 °C cooling water against 10 °C, and recommends controlling it to 10 °C or to 4 °C above seawater. WinGD's X72-B Marine Installation Manual recommends a 25 °C set point for its engines.

Does humidity affect SFOC?

ISO 3046-1:2002 includes 30% relative humidity in its reference state, but neither MAN B&W Table 2.05.02 nor MAN's four-stroke β formula has a humidity term, so the calculator applies no humidity correction.

How is SFOC corrected for fuel calorific value?

Table 2.05.02 gives −1.00% SFOC per 1% rise in lower calorific value against MAN's 42,700 kJ/kg reference. The calculator assumes the input SFOC is already at that reference LCV; convert a figure measured on another fuel first.