Does wrapping a generator's exhaust pipe really save diesel, as the Alwar oil mill manual says?

The Bureau of Energy Efficiency (BEE) Alwar manual says an uninsulated exhaust pipe heats the generator room and hurts the set's efficiency and loading capacity. It books 480 litres of diesel a year, rupees (Rs) 0.168 lakh, for a Rs 3,000 job. It prints no percentage and no baseline litres, so measure yours.

What the manual says

• The exhaust pipes of the diesel generator (DG) sets are not insulated. Heat radiating from them raises the temperature in the DG room.
• The manual's words: high ambient temperature has a very negative effect on the efficiency and loading capacity of DG sets.
• The fix is to insulate the exhaust pipe, for Rs 3,000 in all (Rs 0.03 lakh in the summary table). Saving printed: about 480 litres of oil, meaning diesel, for the Alwar and Sawai Madhopur units, Rs 0.168 lakh.

The sums

• Rs 0.168 lakh over 480 litres is Rs 35 a litre. The manual prices diesel at Rs 32 elsewhere. At Rs 32, 480 litres is Rs 15,360.
• Payback: Rs 3,000 / Rs 16,800 x 12 = 2.1 months. The text says 3 months and the summary table says 2.
• 480 litres is 40 litres a month for a year, which looks like one set (our reading).

What the manual leaves out

• No baseline diesel, no percentage saving and no measurement. A saving in litres with no baseline cannot be checked against your slips.
• Our note, not the manual's: a lagged pipe also lowers the burn risk to anyone who touches it, whatever the fuel saving.

How to test it on your set

1. For a month before, note diesel slips and the DG energy meter's kWh, and work out kWh per litre.
2. Wrap the pipe, and repeat for a month at a similar load.
3. Count only the change in kWh per litre, with the same load. The live page on generator fuel use shows the sum.

The printed saving, checked

• 480 litres x Rs 32 = Rs 15,360 (the manual prints Rs 16,800, which is Rs 35 a litre)
• Payback at Rs 15,360: 3,000 / 15,360 x 12 = 2.3 months
• Carbon dioxide (CO2): 480 x 2.645 kg a litre = 1,270 kg, about 1.3 tonnes a year
• With the test run fix on the sister page: (1,200 + 480) litres x 2.645 = 4,444 kg, about 4.4 tonnes

Litres, price and cost are the manual's, at its date. 2.645 kg of CO2 a litre is the diesel factor Senseible uses: the Intergovernmental Panel on Climate Change 2006 net calorific value and emission factor, with the diesel density of 0.83 kg a litre from the Central Electricity Authority database.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the diesel bought for the set shows by month. It does not read the generator's meter or tell whether the exhaust wrap worked.

• Alwar generator test run diesel
• How many units a diesel generator should give per litre
• Do the Alwar manual totals add up
• Carbon calculators

Sources: Bureau of Energy Efficiency and Confederation of Indian Industry, Manual on energy conservation measures in the Alwar oil mill cluster (SAMEEEKSHA), Intergovernmental Panel on Climate Change, 2006 Guidelines, Volume 2 Energy (fuel emission factors), Central Electricity Authority, CO2 Baseline Database for the Indian Power Sector (grid factor 0.675 kg CO2 per kWh, financial year 2025-26; diesel density 0.83 kg a litre, Appendix B)

Last reviewed 2026-11-06. Figures are the manual's, from the Bureau of Energy Efficiency Small and Medium Enterprises (SME) programme. The saving is an estimate with no baseline; measure kWh per litre before and after.