# What methane and nitrous oxide does the Intergovernmental Panel on Climate Change assume for a diesel locomotive, and does the engine type change it?

Canonical: https://senseible.earth/answers/ipcc-diesel-locomotive-methane-nitrous-oxide-by-engine-type

The Intergovernmental Panel on Climate Change (IPCC) 2006 default for diesel locomotives is 4.15 kilograms of methane (CH4) and 28.6 kilograms of nitrous oxide (N2O) per terajoule (TJ) of fuel. An engine weighting, given for uncontrolled engines, lets you lower the methane figure by up to 20 percent. It does not change the nitrous oxide.

## The rail defaults for diesel and for coal

- Diesel, in kilograms per TJ: carbon dioxide (CO2) 74,100 (range 72,600 to 74,800), CH4 4.15 (range 1.67 to 10.4), N2O 28.6 (range 14.3 to 85.8).
- Sub-bituminous coal, in kilograms per TJ: CO2 96,100 (range 72,800 to 100,000), CH4 2 (range 0.6 to 6), N2O 1.5 (range 0.5 to 5).
- The table notes that the diesel CH4 and N2O figures are for an average fuel use of 0.35 litres per brake horsepower hour in a 4,000 horsepower locomotive, which is 0.47 litres per kilowatt hour for a 2,983 kilowatt locomotive. So the defaults describe a large 4,000 horsepower locomotive, not a small shunter; our reading is that a small siding engine can differ.

## What the engine weighting does

The guide says these non-CO2 defaults may be modified for engine design. Equation 3.4.4 multiplies the default diesel factor by a pollutant weighting factor for the locomotive type. Table 3.4.2 gives those weights for uncontrolled engines, as CH4 then N2O.

Naturally aspirated direct injection: 0.8 and 1.0. Turbo-charged direct injection, or intercooled turbo-charged direct injection: 0.8 and 1.0. Naturally aspirated pre-chamber injection: 1.0 and 1.0. Turbo-charged pre-chamber injection: 0.95 and 1.0. Intercooled turbo-charged pre-chamber injection: 0.9 and 1.0.

Our reading of the table: the best case takes methane down to 80 percent of the default, and every N2O weight is 1.0, so the nitrous oxide default stands for all five engine types.

## Older engines

The guide adds that the default CH4 factors may be increased by 1.5 percent per year to allow for ageing, while the deterioration for N2O is negligible. That rise goes the other way from the engine weighting, so an older engine can end up near or above the default. The text does not say from which year of engine life the 1.5 percent counts, so write down the start year you use.

## Why nitrous oxide is the gas to watch

The road diesel default in the same chapter is 3.9 kilograms of N2O per TJ, so the locomotive figure is about 7.3 times higher. At the example global warming potentials below, the N2O from the locomotive adds about 10 percent to the CO2. The off-road industry row for diesel in Table 3.3.1 uses the same 4.15 and 28.6, so for a siding shunter the choice between the rail and the off-road table does not change the default.

## Three levels of detail

- Tier 1: fuel burnt, as represented by fuel sold, in TJ, times the default factor for that fuel, summed over the fuels used.
- Tier 2: the same sum, but with country-specific factors for each locomotive type, if you have them.
- Tier 3: the number of locomotives of each type, times annual hours of use, times rated power in kilowatts, times load factor, times a factor in kilograms per kilowatt hour, summed over the types and journey types.

## Shunting engine, 20,000 litres of diesel in a year (example quantities)

- CO2: 20,000 x 2.68 = 53,600 kilograms
- Energy: 53,600 / 74,100 kilograms per TJ = 0.723 TJ
- CH4 at the default: 0.723 x 4.15 = 3.00 kilograms. With a weighting of 0.8: 2.40 kilograms
- N2O: 0.723 x 28.6 = 20.7 kilograms
- At example global warming potentials (GWP) of 28 for methane and 265 for nitrous oxide: methane about 84 kilograms of carbon dioxide equivalent (CO2e), nitrous oxide about 5,482 kilograms
- Nitrous oxide against CO2: 5,482 / 53,600 = 10.2 percent

The 20,000 litres, 2.68 kilograms of CO2 per litre and the two GWP values are example numbers. Use the GWP set your report names.

## What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the diesel bought for a shunting engine shows up once uploaded. Which engine design you have, and which table you follow, is your decision to write down.

- [Own locomotive on a private siding: Scope 1](https://senseible.earth/answers/private-railway-siding-locomotive-diesel-scope-1)
- [Methane and nitrous oxide from diesel](https://senseible.earth/answers/methane-n2o-from-diesel-combustion)
- [Tractor and farm machinery diesel](https://senseible.earth/answers/tractor-diesel-emissions-per-acre)
- [Free calculators](https://senseible.earth/calculators)

Sources: [IPCC 2006 Guidelines, Volume 2 chapter 3: Mobile Combustion (Tables 3.3.1, 3.4.1 and 3.4.2)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/2_Volume2/V2_3_Ch3_Mobile_Combustion.pdf)

Last reviewed 2026-11-05. Factors are the 2006 IPCC Tier 1 defaults, which are based on European and North American engine data. The weighting factors are for uncontrolled engines. Confirm with your verifier which table and engine class you follow.