Variable Composition Hydrogen/Natural Gas Mixtures for Increased Engine Efficiency and Decreased Emissions

Abstract

It is well known that adding hydrogen to natural gas extends the lean limit of combustion and that in this way extremely low emission levels can be obtained: even the equivalent zero emission vehicle (EZEV) requirements can be reached. The emissions reduction is especially important at light engine loads. In this paper results are presented for a GM V8 engine. Natural gas, pure hydrogen and different blends of these two fuels have been tested. The fuel supply system used provides natural gas/hydrogen mixtures in variable proportion, regulated independently of the engine operating condition. The influence of the fuel composition on the engine operating characteristics and exhaust emissions has been examined, mainly but not exclusively for 10 and 20 percent hydrogen addition. At least 10 percent hydrogen addition is necessary for a significant improvement in efficiency. Due to the conflicting requirements for low hydrocarbons and low NOx, determining the optimum hythane composition is not straight-forward. For hythane mixtures with a high hydrogen fraction, it is found that a hydrogen content of 80 percent or less guarantees safe engine operation (no backfire nor knock), whatever the air excess factor. It is shown that to obtain maximum engine efficiency for the whole load range while taking low exhaust emissions into account, the mixture composition should be varied with respect to engine load. [S0742-4795(00)02001-9]

Investigation of the Effect of Additives to Natural Gas on Heavy-Duty SI Engine Combustion Characteristics

“…The hydrogen also increases the flame's resistance to stretch (Gauducheau, Denet, & Searby, 1998), reducing local extinction events. At a constant air-fuel ratio, NOx emissions are increased due to a higher adiabatic flame temperature while CO and HC emissions are reduced (Sierens & Rosseel, 2000). Flame stability in the presence of EGR is also improved (Allenby, Chang, Megaritis, & Wyszynski, 2001).…”

A Review of Hydrogen-Natural Gas Blend Fuels in Internal Combustion Engines

“…By the way, as a consequence of a faster combustion, higher temperature are attained in the combustion chamber, increasing NOx emissions in HCNG fuelled engines compared to natural gas, for a given equivalence ratio φ. NOx can be kept down and engine efficiency further improved if the engine is run with lean mixtures or adopting EGR at stoichiometric air-fuel ratio. Sierens & Rosseel (2000) found the maximum NOx emissions at a relative air-fuel ratio λ = 1.1. For higher λ values, the reduction in heat of combustion available for the charge mixture reduces the temperature and NOx as a consequence, as shown in Figure 8.…”

“…6. Engine efficiency versus relative air-fuel ratio λ for different fuels (Sierens & Rosseel, 2000).…”

“…Sierens & Rosseel (2000) developed a fuel system which supplies hydrogen-natural gas mixtures in variable proportion to the engine. For low brake mean effective pressures high efficiency can be achieved by increasing the hydrogen content reducing throttling losses.…”

Performance and Emission Study on a Dual Fuel Engine with Modified Gas Inlet

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