ORIGINAL RESEARCH article
Front. Mech. Eng.
Sec. Engine and Automotive Engineering
The Influence of Diesel Pilot Injection Timing on The Combustion and Emission Characteristics of a Natural Gas-Diesel Dual-Fuel Engine
Provisionally accepted
- Beijing University of Technology, Beijing, China
Select one of your emails
You have multiple emails registered with Frontiers:
Notify me on publication
Please enter your email address:
If you already have an account, please login
You don't have a Frontiers account ? You can register here
This study investigated the effects of varying diesel pilot injection timings (19°-25° BTDC) on the thermal efficiency, combustion, and emission characteristics of an engine operating under different load ranges (25%–100%) using a modified single-cylinder natural gas-diesel dual-fuel (NDDF) engine. The results indicate that advancing the injection timing can significantly improve brake thermal efficiency (BTE) under partial loads (25%–75%), but efficiency decreases at 100% load. Specifically, advancing the timing to 25 ° BTDC results in a reduction in BTE compared to 23 ° BTDC. This suggests that the negative compression work generated by excessively early combustion exceeds the benefits from improved combustion, thereby establishing a physical limit for advanced injection under high-load conditions. Combustion analysis identified a distinct "combustion phase shift" phenomenon. The results show that although advanced injection shifts the combustion phase closer to the favorable high-temperature region near top dead center (TDC), there is only a slight change in combustion duration. This is mechanically attributed to the over-leaning of the pilot diesel spray during prolonged ignition delay. The consequent formation of weak combustion cores slows initial flame propagation, counteracting the accelerating effects of improved thermodynamics. Emission analysis reveals a trade-off: advanced injection reduces smoke emissions by up to 4.2% but substantially increases nitrogen oxides (NOx). Concurrent increases in carbon monoxide (CO) with advanced timing suggest local quenching and over-leaning effects. Additionally, a dynamic fuel substitution strategy was employed to optimize the NDDF engine, successfully maintaining efficiency while mitigating detonation. This study provides a validated experimental basis for the precise calibration of dual-fuel engines across the load range.
Keywords: Brake thermal efficiency, diesel, Dual-fuel engine, Emissions, NATURAL GAS, Pilot injection timing
Received: 05 Nov 2025; Accepted: 28 Nov 2025.
Copyright: © 2025 WU and QIU. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: YUE WU
Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.