A model validated on two engines found that partial fuel switching could reduce direct-use carbon emissions, but the overall benefit depends on how the gas is supplied.
Researchers combined engine experiments, combustion modeling and energy analysis to assess diesel engines adapted to run on both diesel and liquefied petroleum gas. They tested a common-rail engine and a mechanically injected engine, then used the results to estimate potential emissions reductions across a fleet.
The most favorable tested range was a 20–30% share of energy from liquefied petroleum gas. In that range, brake power stayed near the diesel level, specific energy consumption changed little, exergy efficiency rose by about 1.5–2.8%, and smoke decreased. The study’s fleet scenario estimated a 6–9% reduction in direct-use emissions when 30% of vehicles were retrofitted and used an average 25% gas substitution rate.
What the engines showed
The AVL-BOOST combustion model matched experiments closely for the two engine platforms. Predicted torque and specific energy consumption had mean absolute percentage errors below 5%, with R² values of 0.992 for torque and 0.948 for specific energy consumption. Peak in-cylinder pressure differed from measurements by less than 3%.
At 20–30% liquefied petroleum gas energy substitution, brake power remained close to the conventional diesel baseline and specific energy consumption stayed near that baseline. Exergy efficiency, a measure of how much useful energy the engine obtains from its fuel, increased by about 1.5–2.8%, while smoke decreased markedly. The results also showed emission trade-offs: carbon monoxide decreased in the tested conditions, while nitrogen oxides and unburned hydrocarbons were sensitive to combustion timing and low-load oxidation. At substitution rates of 40% or more, nitrogen oxides and hydrocarbons increased, so rates above 30% were not recommended under the study’s control strategy.
Why the fleet estimate matters
The findings suggest that some existing diesel fleets could use a partial fuel switch rather than immediately moving to fully electric vehicles. In the modeled scenario, converting 30% of a fleet and replacing an average 25% of diesel energy with liquefied petroleum gas reduced tank-to-wheel carbon dioxide-equivalent emissions by approximately 6–9%.
That estimate describes emissions during vehicle operation. The wider well-to-wheel benefit is not fixed: it depends on emissions from producing, processing, transporting and distributing the liquefied petroleum gas. The technology is therefore a transitional option whose value must be assessed against the fuel supply conditions in a particular region.
Evidence and caveats
The study combined experiments on two diesel engines with one-dimensional, AVL-BOOST-based combustion modeling and a fleet-level emissions calculation. The model reproduced key performance and combustion measures closely, but the evidence comes from two representative engine platforms and modeled fleet scenarios rather than a field demonstration across an operating fleet.
The engine model uses volume-averaged combustion zones and does not directly capture detailed fuel-mixture patterns inside the cylinder. This limits its ability to resolve some sources of nitrogen oxide, carbon monoxide and hydrocarbon emissions, especially at low load. The reported 6–9% fleet reduction uses a tank-to-wheel boundary. The study included a sensitivity discussion of upstream fuel pathways, but not a complete, region-specific well-to-wheel life-cycle assessment. The authors also identify retrofit cost, maintenance, fuel availability, safety rules and other deployment factors as practical considerations.
// Source
Energy Reports · 2026 · DOI: 10.1016/j.egyr.2026.109753
Authors: Nguyen Tuong Vi, Trieu Quy Huy
