Evaluation of emission characteristics of a stoichiometric natural gas engine fueled with compressed natural gas and biomethane

In this study, the performance and emission characteristics of a stoichiometric natural gas engine were investigated using biomethane and compressed natural gas (CNG). The wide-open throttle (WOT) test and world harmonized transient cycle (WHTC) mode were conducted using a 11 L class six-cylinder natural gas engine that satisfies the emission standards of EURO-6. The biomethane contained 98.69% CH4 content and had a low calorific value of 39.46 MJ/Nm(3) owing to the absence of C2-C4 hydrocarbons. In the WOT test, the engine performance deteriorated due to the poor combustion characteristics of biomethane. In particular, the thermal efficiency decreased by 2% when biomethane was used. The high CH4 content of biomethane increased the concentration of oxygenated hydrocarbons at the engine outlet. A total of 72%-76% of non-methane hydrocarbon (NMHC) was oxygenated in the WOT test using biomethane. In the WHTC mode, the emission standards of EURO-6 for nitrogen oxide, carbon monoxide, and NMHC were satisfied using biomethane. However, CH4 and ammonia emissions were higher than those specified in the EURO-6 emission standards when biomethane was used. Fuel consumption with biomethane was also 39.4% higher than that of CNG during the WHTC mode. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The performance of an engine using biomethane deteriorated in the wide-open throttle test, but it met the EURO-6 emission standards for nitrogen oxide, carbon monoxide, and non-methane hydrocarbons in the world harmonized transient cycle mode. However, methane and ammonia emissions were higher than specified in the EURO-6 standards, and fuel consumption with biomethane was 39.4% higher than with CNG in the WHTC mode.