Abstract
Research and/or Engineering Questions/Objective
Natural gas fuel, as an alternative energy source of transportation, has been used widely since it has an advantage of low emission level. But new technologies are required to be developed to meet the reinforced emission regulations. For this purpose the research for the development of HCNG(Hydrogencompressed natural gas blends) engine has been carried out to evaluate its feasibility and emission characteristics.
Methodology
The Engine Research Department in Korea has carried out a large number of tests with various parameter changes, which can affect the performance and emission of HCNG engine, in different operating conditions. Earlier stage of research project focused on the lean combustion of HCNG engine for heavy duty vehicles to meet the EURO-VI standard. 11-L/6-cylinder CNG engine was used in the test and the effect of excess air ratio change was assessed with the various content ratios of hydrogen in the natural gas fuel. In the later part of HCNG research, stoichiometric mixture operation is suggested to meet reinforced emission regulation without De-NOx system and EGR(Exhaust gas recirculation) is introduced for the purpose of the improvement in thermal efficiency and durability. The optimal operating condition was selected to be that of best thermal efficiency with available emission levels.
Results
In the paper HCNG engine could achieve a significant decrease in NOx emissions, as compared to that of in CNG engine and the EURO-VI standard was satisfied with transient mode cycle test. EGR can suppress the weakness of stoichiometric mixture combustion strategy, such as the deterioration of durability and thermal efficiency, while the emission level can be lowered with the use of three way catalyst. The possibility of further reduction of emission and CO2 with EGR was evaluated to access practical application of HCNG engine in the field.
Limitations of this study
An important limitation of the current study is the limited bench test in the dynamometer tests. Furthermore, the introduction of EGR was restrained in low pressure loop from a proto-type module environment.
What does the paper offer that is new in the field including in comparison to other work by the authors?
The development and strategies with HCNG presented in this paper are new as well the resulting low emission requirements for future emission regulation.
Conclusions
The HCNG engine with stoichiometric mixture operation for heavy duty vehicles has been developed. The emission level of HCNG engine shows lower by 50% compared to EURO-VI standard and more than 10% of CO2 decreased compared to that of natural gas engine.
Key Words : HCNG; Lean Combustion; Stoichiometric; EGR; CO2