Internal combustion engines fueled by natural gas—hydrogen mixtures

Catalytic reforming of methane (CH4) with carbon dioxide (CO2), known as dry reforming of methane (DRM), produces synthesis gas, which is a mixture of hydrogen (H2) and carbon monoxide (CO). CH4 + CO2 → 2CO + 2H2, ΔH° = 247.3 kJ mol−1, ΔG = 61 770–67.32T. The DRM process has gained much attention recently as it reduces greenhouse gases (GHG), CO2 and CH4, in the atmosphere. In addition to reducing GHG, the DRM process produces valuable chemicals (CO + H2), provides a good approach to utilizing biogas and natural gas with a significant amount of CO2, has good capability as a chemical energy transmission system as compared to steam reforming, and finally yields the desired unity H2/CO ratio for Fischer–Tropsch synthesis. The bimetallic Ni-based catalysts supported on Al2O3/TiO2 and promoted with Ce/ZrO2 show remarkable performances in the DRM process. But, carbonaceous deactivation of the catalysts is the major problem faced during this process. Numerous studies have been cited on various aspects of DRM, and some papers are also devoted to reviewing carbonaceous deposition problems and their remedies. However, some lacunae exist, which are highlighted in the present review paper on strategies to reduce the carbonaceous deactivation of catalysts for improved DRM efficiency by appropriate catalyst development, operating conditions, and flow reactor designs. The disposal of spent catalysts falls under the category of hazardous industrial materials and is also required to comply with stringent environmental regulations. Therefore, regeneration and reclamation techniques for spent catalysts have also been discussed.

An overview on dry reforming of methane: strategies to reduce carbonaceous deactivation of catalysts

Combustion characteristics of a direct-injection engine fueled with natural gas–hydrogen blends under different ignition timings

Investigation of combustion characteristics and emissions in a spark-ignition engine fuelled with natural gas–hydrogen blends

With the huge growing demand of energy utilization and various threats posed due to the emissions had substantially led the thinkers to put on strategic plans to decrease the usage of energy and reduce the carbon contents of fuels. Moving ahead with these plans hydrogen enriched compressed natural gas (HCNG) engines have emanated as a forthcoming energy carrier for internal-combustion engines. Several nations are endeavoring hard to bring down the pollution level by promoting hydrogen enriched compressed natural gas-fueled vehicles, predominantly by powering medium and heavy transportation vehicles. In general, under precise circumstances the indicated thermal efficiency of the HCNG engine is much better than CNG engines without tolerating the high level of harmful emissions. In spite of that the hydrogen addition to NG provides increased NOx emission because of a great amount of heat generation inside the combustion chamber. However, it can be overcome by some extent of the application of lean burn combustion or with three-way catalyst (TWC). This report presented an encyclopedic overview of hydrogen enriched compressed natural-gas engines. This paper provides a detailed discussion on the hydrogen generation methods, fundamentals of characteristics of HCNG mixture, refinements on different fuel mixture affecting the combustion. For covering the prospects of the HCNG engines, its technical and numerical approaches are discussed. Furthermore, various methods are discussed which increase the power output and thermal efficiency along with a check on the emission parameters. An exploration of HCNG vehicle's demonstration projects worldwide is a key feature of this article.

Progress in hydrogen enriched compressed natural gas (HCNG) internal combustion engines - A comprehensive review

Characteristics of combustion and emissions in a methane direct injection stratified charge engine premixed with hydrogen lean mixture were analyzed. Results showed the combustion system achieved a higher thermal efficiency due to higher flame propagation velocity and lower exhaust emissions. An increase in the amount of premixed hydrogen stabilizes the combustion to reduce HC and CO exhaust emission, and increases the degree of constant volume combustion and NOx exhaust emission. The increase in NOx emission can be maintained at a lower level with retarded ignition timing without deteriorating the improved thermal efficiency.

Kazuki Shimamura

Papers

Combustion and emissions in a methane di stratified charge engine with hydrogen pre-mixing.