A method for determining hydrogen–methane–nitrogen mixtures for laboratory tests of syngas-fuelled internal combustion engines

Abstract

An original method for formulating surrogate fuels from actual syngas mixtures is presented and formalised. The method is the first example in the scientific literature of a rather complete tool for planning and setting up a laboratory syngas-fuelled engine test when some components of the syngas mixture are not available. Basically, the method allows a map to be built that provides the composition for a surrogate fuel once the composition of a syngas mixture is assigned, the components of a surrogate fuel are selected and the equivalence parameters are defined. The laminar flame speed, the energy density of the fuel–air mixture and the methane number are identified as equivalence parameters in the study. In particular, the proper laminar flame speed and energy density ensure that an engine fuelled by the surrogate mixture produces the same indicated power as it would when fuelled by the original syngas. Instead, the methane number allows for checking the fact that the tendency of the engine to knock is the same or greater than the knock tendency during syngas operation. In this article, the method is used to determine the hydrogen–methane–nitrogen mixtures corresponding to six five-component syngas mixtures, resulting from actual gasification processes. The laminar flame speed and methane number of each syngas mixture are estimated by means of simple original models aimed at either improving the predicting capabilities of existing models or allowing for a prompt application of the procedure. The results show that four of the six surrogate fuels are equally or more knock-prone than the original syngas mixtures, whereas only one of the two remaining surrogate fuels likely imposes a retardation of the spark advance in the final setup of the engine for actual syngas operation.

Experimental Study and Optimisation of a Non-Conventional Ignition System for Reciprocating Engines Operation with Hydrogen–Methane Blends, Syngas, and Biogas

“…As stated in Introduction, three-species surrogate mixtures made of hydrogen, methane, and nitrogen were used. Their compositions were specifically defined to simulate the three real syngas fuels of Table 2 according to the method suggested by Gobbato et al [21]. The method states that a surrogate mixture must allow the engine to achieve the same power output and fuel conversion efficiency as when the engine is fuelled with the real syngas.…”

“…The square brackets in Equation ( 4) indicate the volume concentration of the species they enclose, whereas the values of coefficients were calculated by a regression analysis of measured data (see [21] for details). Resulting values are: p = 1.2574; q = 0.4605; s = 0.6398; t = −0.2068; u = −0.0284.…”

“…Once the LHV s,mix and the S L of the real syngas are estimated, the composition of the corresponding three-component surrogate mixtures can be derived from the diagram of Figure 2. The diagram is an extended version of the one presented in [21], which relates the couple of values S L -LHV s,mix of a real syngas mixture to the two parameters α and β of its corresponding surrogate H 2 -CH 4 -N 2 mixture. The first parameter α is defined as the H2 to H2-CH4 volume ratio, whereas β is defined as the ratio between the non-reacting syngas fraction (simulated with a volume of N2) and the entire fresh charge (i.e., the air volume plus the volume of the non-combustible components).…”

“…It is worth noting that the EQTF mixture also shows α = 0.6 and so it can be obtained using the same H 2 -CH 4 tank selected for the surrogate syngas mixtures. Finally, according to the method presented in [21], the equivalent fuel mixtures so obtained must be checked against the methane number (MN). The MN is defined as the percentage of methane in a methane-hydrogen mixture which has the same resistance to knock as the actual mixture.…”

“…On the other hand, surrogate mixtures may avoid safety concerns during the testing activity related to the toxicity of carbon-monoxide present in real syngas fuels. Therefore, the experimental activity of the present study was carried out using surrogate mixtures, which do not contain CO and are made of H 2 , CH 4 , and N 2 , with a composition defined in accordance with the method suggested by the authors in a previous work [21].…”