Material Insights · Understanding the Material World

Engine exhaust recovery: Impact and additionality

Real fuel savings inside a fleet heading for retirement

What this tab covers The impact and additionality lens: direct emission cuts, side benefits for water and air, and the risk of prolonging the life of a polluting host plant.

Exhaust recovery cuts fuel and CO2 by a few per cent per engine, which is large across a fleet, but it extends the life of diesel and gas engines.

Direct Scope 1 and Scope 2 abatement

Mixed

Because the saving is fuel burned on board, it is a direct Scope 1 cut: a 5-7.5% fuel saving from turbo-compounding gives the same percentage cut in tailpipe CO2 for a given duty (calculated). Turbocharging's contribution is embedded in the baseline efficiency of today's 46-53% diesels. For engine power plants, raising efficiency from 48% to 50% cuts fuel per MWh by about 4% (calculated). On ships, an Accelleron turbocharger upgrade trial with COFCO averaged 3.5% fuel saving over 13 voyages, saving 327 t of fuel and 1,030 t CO2 (company data).12611

Turbo-compound CO2 cut about 5-7.5% (calculated)12 Engine plant fuel cut, 48% to 50% efficiency about 4% (calculated)6 COFCO voyage trial (company data) 3.5% fuel saving; 1,030 t CO2 over 13 voyages11

Water and air synergy

Mixed

Turbocharging allows leaner, more complete combustion and supports the high boost needed by low-emission engines, but hotter, higher-pressure combustion raises NOx that aftertreatment must remove. Recovering exhaust energy downstream can cool the gas below what catalysts need, so systems must be designed together. Steam bottoming on engine plants needs water or air cooling.34

Avoided lock-in

Unfavourable

Turbo-compounding improves the economics of long-haul diesel trucks and gas engine plants, which could slow the switch to zero-emission alternatives. Its value depends on the fossil engine staying in service. For an impact investor it is an efficiency gain inside an asset class that is being phased down, not a transition technology.1

Sources

  1. OEMs mixed on turbo compounding Transport Topics, 2018
  2. Detroit Diesel DD15 debuts with better fuel economy and performance (2007, dated) Heavy Duty Trucking (truckinginfo.com), 2007
  3. Reciprocating Engines, CHP Technology Fact Sheet Series (DOE/EE-2764) US Department of Energy, 2023
  4. Comparative analysis of the heat balance results of the selected Tier III-compliant gas-fuelled two-stroke main engines (Korlak), Combustion Engines 193(2) Combustion Engines (journal), 2023
  5. Wartsila's latest combustion engine offers new options for intermediate capacity POWER Magazine, 2012
  6. Annual Report 2025 (company-reported figures and claims) Accelleron Industries, 2026