Use of catalytic reforming to aid natural gas HCCI combustion in engines: experimental and modelling results of open-loop fuel reforming

Abstract

The potential of the homogeneous charge compression ignition (HCCI) combustion process to deliver drastically reduced emissions of NO x and improved fuel economy from internal combustion engines is well known. The process is, however, difficult to initiate and control, especially when methane or natural gas are used as fuel. To aid the HCCI combustion of natural gas, hydrogen addition has been successfully used in this study. This hydrogen can be obtained from on-line reforming of natural gas. Methane reforming is achieved here by reaction with engine exhaust gas and air in a small scale monolith catalytic reactor. The benchmark quantity of H 2 required to enhance the feasibility and engine load range of HCCI combustion is 10%. For low temperature engine exhaust gas, typical for HCCI engine operating conditions, experiments show that additional air is needed to produce this quantity. Experimental results from an open-loop fuel exhaust gas reforming system are compared with two different models of basic thermodynamic equilibria calculations. At the low reactor inlet temperatures needed for the HCCI application (approx. 400 ∘ C ) the simplified three-reaction thermodynamic equilibrium model is in broad agreement with experimental results, while for medium ( 550 – 650 ∘ C ) inlet temperature reforming with extra air added, the high hydrogen yields predicted from the multi-component equilibrium model are difficult to achieve in a practical reformer.