Wobbe Index Research Articles

Dynamic biogas upgrading based on the Sabatier process: Thermodynamic and dynamic process simulation

This study aimed to investigate the feasibility of substitute natural gas (SNG) generation using biogas from anaerobic digestion and hydrogen from renewable energy systems. Using thermodynamic equilibrium analysis, kinetic reactor modeling and transient simulation, an integrated approach for the operation of a biogas-based Sabatier process was put forward, which was then verified using a lab scale heterogenous methanation reactor. The process simulation using a kinetic reactor model demonstrated the feasibility of the production of SNG at gas grid standards using a single reactor setup. The Wobbe index, CO2 content and calorific value were found to be controllable by the H2/CO2 ratio fed the methanation reactor. An optimal H2/CO2 ratio of 3.45–3.7 was seen to result in a product gas with high calorific value and Wobbe index. The dynamic reactor simulation verified that the process start-up was feasible within several minutes to facilitate surplus electricity use from renewable energy systems.

Air quality impacts of liquefied natural gas in the South Coast Air Basin of California

The effects of liquefied natural gas (LNG) on pollutant emission inventories and air quality in the South Coast Air Basin (SoCAB) of California are evaluated using recent appliance emissions measurements by Lawrence Berkeley National Laboratory and the Southern California Gas Company (SoCalGas), and use of a state-of-the-art air quality model. Pollutant emissions can be impacted by LNG operation because of differences in composition and physical properties including the Wobbe index, a measure of energy delivery rate. Various LNG distribution scenarios are evaluated to determine the potential impacts of LNG. Projected penetration of LNG in the SoCalGas pipeline network in SoCAB is expected to be limited, which could cause increases in overall (area-wide) emissions of nitrogen oxides that are smaller than 0.05%. Based on the photochemical state of the South Coast Air Basin of California, any increase in NOx is expected to cause an increase in the highest local ozone concentrations, which is observed in model results. However, the magnitude of NOx emissions increases due to LNG use is determined to be within the uncertainty range of natural gas combustion sources and would not be discernible with the existing monitoring network.

Flame stability of partially premixed combustion for PNG/LNG interchangeability

In this paper, the flame stability of partially premixed combustion for pipeline natural gas (PNG) and liquefied natural gas (LNG) interchangeability was investigated. A wide range of primary air ratio was considered and the characteristics of yellow flame and lifted flame were emphasized. The effect of gas flame speed (Sn), flame inner core height (h), gas flow rate (Lg), air flow rate (La), port thermal intensity (qp) and burner head temperature were discussed. Experiments showed that flame speed and flame inner cone height were mainly affected by gas components and lifted flame was influenced by flame speed and burner head temperature. When gases were interchanged, the flame speed and lifted flame could not be simply predicted by Wobbe index. When gas wobbe index increased, more chances yellow flame would appear and the gases with similar wobbe indexes have similar performance of yellow flame characteristics.

Combustion Optimisation using Methane Number and Wobbe Index as Evaluation Criteria

One hundred and ten (110) streams have been identified in an oil refining process as contributors to the gas fuel net used in furnaces and boilers to supply power and steam to process. According to the origin of the gases and the previous treatment, these gas streams, have a different composition than the natural gas, which creates problems that affect the operational parameters and the integrity of equipment. It is due to this, which seeks to analyse how the fuel gas flows from a refining process, taking into account the energy efficiency, environmental and safety aspects in combustion process. Statistical analysis was developed in combustible gases to study their composition considering the origin of each of the streams represented by chromatographic analysis, which, provided the data for calculating the methane’s number (MN) via method radius ratio (H/C), and the Wobbe index as criteria for analysing the potential effect of gas fuel composition in efficiency, integrity and environmental emissions equipment. The methane’s number is a parameter which describes the behaviour of the explosive self-initiated and not controlled combustion in gas zone of the front flame (referred as knock Combustion). This knock resistance index, has two reference gases, methane and hydrogen; using a reference fuel mixture in which the methane works with a MN 100 and hydrogen with a MN 0. High numbers of MN means high efficiency and hence lower CO2. If MN is too low, knock can cause damage or loss in efficiency and performance. The results show that 45% of the streams of petrochemical area presented MN above 80 and 15% of streams presented low MN. Streams of cracking area showed lower MN. These results demonstrate the heterogeneity of currents, so that the methane number is an important reference when defining the logistic for combustible net in combustion process. Elaborating further on the effects that this variability can generate in the thermal efficiency of each of the currents, so as combustion efficiency and the stability of the operation was evaluated Wobbe Index, and the results showed that when applying these two methods and taking into account the current regulations, a comprehensive analysis can be performed of energy issues, environmental and security in combustion process of fuel variable composition. The principal result was a proposal for a fuel net.

Method of Measurement and Computing for Natural Gas Energy

Energy measurement and computing can directly reflect the value of natural gas. In our country the volume flow measurement and computing will be gradually replaced by energy measurement. In this paper the principle of energy metering of natural gas is introduced and the system of energy metering of natural gas is constructed. Based on GB/T 11062, computing method of gas energy is discussed, in which quality data of natural gas, temperature, flow, pressure parameters are measured by energy metering system and the calorific value of natural gas, relative density and Wobbe index are and computed. Also the uncertainty of and computing method for natural gas energy is analyzed in which uncertainty is within 0.1%. The results show that the uncertainty of the calorific value measurement system attained accuracy requirements of GB/T 18603-2001.

Laminar flame speed and markstein length characterisation of steelworks gas blends

An outwardly propagating spherical flame configuration has been used to characterise the combustion of different blended steelworks gas compositions, under atmospheric ambient conditions. A nonlinear extrapolative technique was used to obtain values of laminar burning speed and Markstein length for combustion with air and change in equivalence ratio. Peak burning speed was shown to reach almost 1ms−1 for the combustion of coke oven gas under marginally rich conditions, and the influence of flame stretch on burning speed also shown to increase with equivalence ratio. The molar fraction of coke oven gas (COG) was then blended in the range 0–15% with four blast furnace gas mixtures (BFG) containing 1–7% H2 fractions, representative of the inherent compositional fluctuation experienced in production. Profiles for change in burning speed resulting from this addition of COG are presented, and the dampening extent of fluctuation resulting from the H2 variation has been quantified. Results are also presented for the relative change in gross calorific value and corresponding Wobbe index of the variable blended gases across the tested limits. Modelled results were generated using the PREMIX coded CHEMKIN-PRO, and the performance of specified chemical reaction mechanisms evaluated relative to the experimental data.

Hydrogen-enriched non-premixed jet flames: Analysis of the flame surface, flame normal, flame index and Wobbe index

A non-premixed impinging jet flame is studied using three-dimensional direct numerical simulation with detailed chemical kinetics in order to investigate the influence of fuel variability on flame surface, flame normal, flame index and Wobbe index for hydrogen-enriched combustion. Analyses indicate that the fuel composition greatly influences the H2/CO syngas combustion, not only on the important local stoichiometric iso-mixture fraction surface distribution but also on the vortical structures in the flow field. As a result of CO addition to hydrogen-rich combustion, changes of the reaction zone in the flammable layer, shift of peak flame surface density distribution, shift of non-premixed regions, formation of widely populated scalar dissipation distribution rate with respect to tangential strain and reduction of global heat release are all found to appear. In particular, the CO addition induces a micromixing process which appears to be an important factor for the modelling investigation of turbulence/chemistry interaction especially for combustion modelling of H2-rich syngas fuels.

Effect of Change in Fuel Compositions and Heating Value on Ignition and Performance for Siemens SGT-400 Dry Low Emission Combustion System

The influence of changes in fuel composition and heating value on the performance of an industrial gas turbine combustor was investigated. The combustor tested was a single cannular combustor for Siemens SGT-400 13.4 MW dry low emission engine. Ignition, engine starting, emissions, combustion dynamics, and flash back through burner metal temperature monitoring were among the parameters investigated to evaluate the impact of fuel flexibility on combustor performance. Lean ignition and extinction limits were measured for three fuels with different heat values in term of Wobbe Index (WI): 25, 28.9, and 45 MJ/Sm3 (natural gas). The test results show that the air fuel ratio at lean ignition/extinction limits decreases and the margin between the two limits tends to be smaller as fuel heat value decreases. Engine start tests were also performed with a lower heating value fuel and results were found to be comparable to those for engine starting with natural gas. The combustor was further tested in a high pressure air facility at real engine operating conditions with different fuels covering WIs from 17.5 to 70 MJ/Sm3. The variation in fuel composition and heating value was achieved in a gas mixing plant by blending natural gas with CO2, CO, N2, and H2 (for the fuel with WI lower than natural gas) and C3H8 (for the fuel with WI higher than natural gas). Test results show that a benefit in NOx reduction can be seen for the lower WI fuels without H2 presence in the fuel and there are no adverse impacts on combustor performance except for the requirement of higher fuel supply pressure, however, this can be easily resolved by minor modification through the fuel injection design. Test results for the H2 enriched and higher WI fuels show that NOx, combustion dynamics and flash back have been adversely affected and major change in burner design is required. For the H2 enriched fuel, the effect of CO and H2 on combustor performance was also investigated for the fuels having a fixed WI of 29 MJ/Sm3. It is found that H2 dominates the adverse impact on combustor performance. The chemical kinetic study shows that H2 has significant effect on flame speed change and CO has significant effect on flame temperature change. Although the tests were performed on the Siemens SGT-400 combustion system, the results provide general guidance for the challenge of industrial gas turbine burner design for fuel flexibility.

Gaseous components from pyrolysis—Characteristics, production and potential for energy utilization

This article is focused on a complex evaluation of the process gas produced within an experimental pilot-scale system which thermally processes input materials by a form of pyrolysis. The Pyromatic system is a unique device. Its originality consists in its ability to continually process secondary organic raw materials. Within the Czech Republic, it does not have any parallel to its power output (it can process up to 150kg of input material per hour) and its design.The presented results and conclusions show the product yield and characteristics of the gaseous product from this system with regard to a selected input material and process conditions. Three kinds of material were chosen for pyrolysis—biomass, brown coal, and rubber. Attention was especially focused on the gas quality related to energy and its combustion characteristics. The aim was to introduce all important characteristics (gross calorific value, flammability limit, propagation rate, Wobbe index, combustion potential, etc.) that adumbrate the possibilities and potential of this gas utilization in the power industry.

Influence of reactive species on the lean blowout limit of an industrial DLE gas turbine burner

In order to achieve ultra-low emissions of both NOX and CO it is imperative to use a homogeneous premixed combustor. To lower the emissions further, the equivalence ratio can be lowered. By doing so, combustion is moved towards the lean blowout (LBO) limit. To improve the blowout characteristics of a burner, heat and radicals can be supplied to the flame zone. This can be achieved using a pre-chamber combustor. In this study, a central body burner, called the RPL (rich-pilot-lean) section, was used as a pre-chamber combustor to supply heat and radicals to a downscaled industrial burner. The flue gas from the RPL is mixed with the surrounding fresh mixture and form a second flame zone. This zone acts as a stabilizer for the investigated burner. The LBO limit was modeled using two perfectly stirred reactors (PSRs) in series, which allows the chemical influence on the LBO limit to be isolated. The resulting trends for the modeled LBO limit were in agreement with measured data. Increasing the equivalence ratio in the RPL section, thus increasing the energy supplied by the fuel, is a major contributor to combustion stability up to a limit where the temperature decrease is too large support combustion. For lean RPL combustion, the reactive species O, H and OH in combination affect the stability to a greater extent than the temperature alone. At rich equivalence ratios, the conversion of methane to hydrogen and carbon monoxide in the RPL section is a factor influencing the LBO limit. The results are compared with emission probe measurements that were used to investigate the LBO limit for methane and a generic syngas (10% CH4, 67.5% H2, and 22.5% CO). The syngas was also investigated after being diluted with nitrogen to a Wobbe index of 15MJ/m3.

TDLAS-based sensors for in situ measurement of syngas composition in a pressurized, oxygen-blown, entrained flow coal gasifier

Tunable diode laser absorption spectroscopy based in situ sensors for CO (2.33 μm), CO2 (2.02 μm), CH4 (2.29 μm) and H2O (1.35 μm) were deployed in a pilot-scale (1 ton/day), high-pressure (up to 18 atm), entrained flow, oxygen-blown, slagging coal gasifier at the University of Utah. Measurements of species mole fraction with 3-s time resolution were taken at the pre- and post-filtration stages of the gasifier synthesis gas (called here syngas) output flow. Although particulate scattering makes pre-filter measurements more difficult, this location avoids the time delay of flow through the filtration devices. With the measured species and known N2 concentrations, the H2 content was obtained via balance. The lower heating value and the Wobbe index of the gas mixture were estimated using the measured gas composition. The sensors demonstrated here show promise for monitoring and control of the gasification process.

Multi-species laser absorption sensors for in situ monitoring of syngas composition

Tunable diode laser absorption spectroscopy sensors for detection of CO, CO2, CH4 and H2O at elevated pressures in mixtures of synthesis gas (syngas: products of coal and/or biomass gasification) were developed and tested. Wavelength modulation spectroscopy (WMS) with 1f-normalized 2f detection was employed. Fiber-coupled DFB diode lasers operating at 2325, 2017, 2290 and 1352 nm were used for simultaneously measuring CO, CO2, CH4 and H2O, respectively. Criteria for the selection of transitions were developed, and transitions were selected to optimize the signal and minimize interference from other species. For quantitative WMS measurements, the collision-broadening coefficients of the selected transitions were determined for collisions with possible syngas components, namely CO, CO2, CH4, H2O, N2 and H2. Sample measurements were performed for each species in gas cells at a temperature of 25 °C up to pressures of 20 atm. To validate the sensor performance, the composition of synthetic syngas was determined by the absorption sensor and compared with the known values. A method of estimating the lower heating value and Wobbe index of the syngas mixture from these measurements was also demonstrated.

Laminar burning velocity and interchangeability analysis of biogas/C3H8/H2 with normal and oxygen-enriched air

Numerical and experimental measurements of the laminar burning velocities of biogas (66% CH4 – 34% CO2) and a biogas/propane/hydrogen mixture (50% biogas – 40% C3H8 – 10% H2) were made with normal and oxygen-enriched air while varying the air/fuel ratio. GRI-Mech 3.0 and C1–C3 reaction mechanisms were used to perform numerical simulations. Schlieren images of laminar premixed flames were used to determine laminar burning velocities at 25 °C and 849 mbar. The mixture's laminar burning velocity was found to be higher to that of pure biogas due to the addition of propane and hydrogen. An increase in the laminar burning velocities of both fuels is reported by enriching air with oxygen, a phenomenon that is explained by the increased reactivity of the mixture. Additionally, an analysis of interchangeability based on both the Wobbe Index and the laminar burning velocity between methane and a biogas/propane/hydrogen mixture is presented in order to consider this mixture as a substitute for natural gas. It was found that the variations of these properties between the fuels did not exceed 10%, enabling interchangeability.

Effect of various gas compositions on gas interchangeability and combustion characteristics for domestic appliances

In this study, an investigation into the gas interchangeability and combustion characteristics of various gas compositions for domestic appliances was performed. In order to suggest the appropriateness of gas interchangeability using the specific gravity (SG) and the Wobbe index (WI) values, combustion characteristics included incomplete combustion and flame lifting were measured and observed for the upper and lower limits using the gas-oven as a domestic partial-premixed type appliance and the condensing boiler as a domestic premixed type appliance. The flame was stable, and the CO and NOx concentrations increased when the WI and SG values increased. Specifically, the behavior of the flame lifting changed between WI values of 52.0 MJ/Nm3 and 53.0 MJ/Nm3. The CO and NOx concentrations of the reference gas were approximately 173 ppm and 74 ppm for the gas-oven and 175 ppm and 35 ppm for the boiler, respectively. Consequently, a WI value of 53.0 MJ/Nm3 can be considered the flame lifting limit as the lower limit for gas interchangeability. For the upper limit of gas interchangeability, the CO and NOx concentrations varied significantly with the type of burner.

Flame stability and OH and CH radical emissions from mixtures of natural gas with biomass gasification gas

In this work, a study about laminar premixed flames derived from the combustion of natural gas and producer gas (25 and 50% by volume) mixtures in an atmospheric burner was carried out. The producer gas was obtained from steam gasification process of dealcoholised marc of grape in a small-scale drop-tube gasification pilot plant, this solid fuel being an abundant biomass waste in Spain. These mixtures have different advantages such as replacing fossil fuels with renewable fuels, reducing NOx emissions and other advantages associated with the biomass consumption. The main objectives of this work are to delimitate the stability diagram of the different mixtures, to evaluate the potential of these mixtures to reduce NOx emission and to study the interchangeability of the gas mixtures used. The results obtained show that an increase in the producer gas amount (and therefore in the hydrogen content) makes possible a stable burner operation at leaner conditions, thus leading to lower combustion temperature and NOx emissions. OH and CH radical concentrations were measured by chemiluminescence to confirm the potential to reduce NOx emissions. The Wobbe index results show a possible interchangeability between natural gas and natural gas/producer gas mixtures below 37% vol. of producer gas.

Extension of Fuel Flexibility in the Siemens Dry Low Emissions SGT-300-1S to Cover a Wobbe Index Range of 15 to 49 MJ/Sm3

The extension of gas fuel flexibility in the Siemens SGT-300 single shaft (SGT-300-1S) is reported. A successful development program has increased the capability of the Siemens Industrial Turbomachinery, Lincoln (SITL) dry low emissions (DLE) burner configuration to a fuel range covering a Wobbe index (WI) from 15 to 49 MJ/Sm3. The WI reported in this paper is at a 15 °C fuel temperature. The standard SGT-300-1S SITL DLE combustion hardware allows for gas and liquid fuels within a specified range typically associated with natural gas and diesel, respectively. The range of the WI associated with natural gas is 37–49 MJ/Sm3. Field operation of the standard production SGT-300-1S has confirmed the reliable operation with an extension to the fuels range to include processed landfill gas (PLG) from 30 to 49 MJ/Sm3. The further extension of the fuel range for the SGT-300-1S SITL DLE combustion system was achieved through high pressure testing of a single combustion system at engine operating conditions and representative fuels. The variations in the fuel heating value were achieved by blending natural gas with diluent CO2 and/or N2. Various diagnostics were used to assess the performance of the combustion system, including the measurement of combustion dynamics, temperature, fuel supply pressure, and the emissions of NOx, CO, and unburned hydrocarbons (UHCs). The results of the testing showed that the standard production burner can operate for a fuel with a WI as low as 23 MJ/Sm3, which corresponds to 35% CO2 (by volume) in the fuel. This range can be extended to 15 MJ/Sm3 (54.5% CO2 in the fuel) with only minor modification to control losses through the burner and to maintain similar fuel injection characteristics. The SITL DLE combustion system is able to cover a WI range of 15 to 49 MJ/Sm3 in two configurations. The results of testing showed a lowering in the WI, by diluting with CO2 and/or N2, so that a benefit in the NOx reduction is observed. This decrease in the WI may lead to an increased requirement of the fuel supply pressure.

Experimental research on performance response of domestic gas cookers to variable natural gas constituents

In China, the imported Liquefied Natural Gas (LNG) has been steadily increased in past years, with its constituents different from those of traditional pipeline natural gases (PNG) to various extents. In this paper several natural gases to be delivered to Guangdong provinces in China were selected as test gases to measure performance response of 17 sets of domestic gas cookers. Heat input rating, CO and NOx emission, and thermal efficiency was measured according to related national standards. American Gas Association indexes and Weaver indexes were used to predict combustion stability and emission under different gas constituents. Experiment results were compared with prediction to analyze the applicability of the two well-established indexes systems. It was concluded that Wobbe Index can predict heat input rating quite accurately, and CO and NOx emissions can be remained with reasonable limits for the changing constituents discussed. For combustion stability prediction, judgment criteria should be adjusted as follows: Weaver lifting index from JL ≥ 0.64 to JL ≥ 0.95, Weaver incomplete combustion index from JI ≤ 0.05 to JI ≤ 0.04, and AGA lifting index from IL ≤ 1.10 to IL ≤ 1.05.

Properties of Artificial Gaseous Mixtures for their Safe Use and Support the Natural Gas Supply Networks / Własności Sztucznych Mieszanin Gazowych do Bezpiecznego ich Użytkowania i Wspomagania Zasilania Sieci Gazu Ziemnego

Abstract The increase in natural gas consumption by the general public and industry development, in particular the petrochemical and chemical industries, has made increasing the world interest in using gas replacement for natural gas, both as mixtures of flammable gases and gas mixtures as LPG with air (SNG - Synthetic Natural Gas). Economic analysis in many cases prove that to ensure interchangeability of gas would cost less than the increase in pipeline capacity to deliver the same quantity of natural gas. In addition, SNG systems and installations, could be considered as investments to improve security and flexibility of gas supply. Known existing methods for determining the interchangeability of gases in gas gear based on Wobbe index, which determines the heat input and the burning rate tide, which in turn is related to flame stability. Exceeding the Wobbe index of a value increases the amount of carbon monoxide in the exhaust than the permissible concentration. Methods of determining the interchangeability of gases is characterized by a gas in relation to the above-described phenomena by means of quantitative indicators, or using diagrams interchangeability, where the gas is characterized by the position of a point in a coordinate system. The best known method for determining the interchangeability of gases is Delbourg method, in which the gas is characterized by the revised (expanded) Wobbe Index (Wr), the combustion potential, rate of soot formation (Ich) and the ratio of the formation of yellow ends (Ij). Universal way to determine the interchangeability of gas is also Weaver accounting method. It does not require determination of the reference gas. It is designed for utensils for household gas and gas pressure p = 1.25 kPa. The criteria and definition of gas interchangeability volatility in practice to the combustion in a gas gear. In the case of gas exchange in industrial furnaces, interchangeability criteria are usually not very useful because of other conditions of combustion and heat exchange. In industrial reheating furnace gas is combusted in a sealed combustion chambers. Air supply is regulated. The exhaust gases are discharged into canals and the chimney to the atmosphere. The temperature difference between load (fuel gas) and the flame is much less than in the case of gas household appliances. In the furnace heat exchange takes place mainly by radiation in 85% to 95%. The value of heat flux flowing from the gas to a heated charge is not proportional to the heat load burners. Interchangeability of gas is linked by adding to natural gas, a certain amount of gas that is a substitute for natural gas in meeting the criteria for substitution in order to ensure certainty of supply of natural gas to customers. Gases that can be used in the processes of blending and used as replacement gases are mainly a mixture of propane and propane - butane (LPG - Liquid Petroleum Gas), landfill gas or biogas (LFG - Landfill Gas) and dimethyl ether (DME). One of the more well-known gas mixtures used in many countries around the world to compensate for peak demands is a mixture containing about 75% of natural gas and approximately 25% propane / air (LPG / air). Also in Poland is prepared to amend the provisions in this regard (at this moment - oxygen in the gas network can not exceed 0.2%). In this paper, the calculations of interchangeability of gas mixtures LFG - LPG and LPG - air (SNG) for natural gas was made. It was determined whether the analyzed mixtures have similar stable flame zones regardless of the quality of LFG fuel and whether they may in whole or in part replace CH4, without any modification of equipment suction air for combustion. The obtained results will determine whether the fuel can be used as a replacement for natural gas used in such household appliances and, possibly, industrial burners. In connection with the possibility of changes in the quality of LFG, depending on such factors as storage time, as pre-treatment, will be determined the degree of interchangeability of LFG as a fuel mixed with regard to its quality.

A Micro Gas Turbine Fuelled by Methane-Hydrogen Blends

The combustion efficiency and the gaseous emission of a 100 kWe MGT, designed for working with natural gas but fuelled with blends containing up to 10% of hydrogen is investigated. A critical comparison between experimental data and results of the CFD analysis of the combustor is discussed. The k-epsilon RANS turbulence model and the Finite Rate – Eddy Dissipation combustion model were used in the numerical computations. The chemical kinetic mechanisms embedded were the 2-step Westbrook and Dryer for methane oxidation, 1-step Westbrook and Dryer for hydrogen oxidation and the Zeldovich mechanism for NO formation. The experimental data and numerical computations are in agreement within the experimental accuracy for NO emissions. Regarding CO, there is a significant deviation between experimental and computational data due to the scarce predictive capability of the simple two steps kinetic mechanism was adopted. From a practical point of view, the possibility of using fuels with a similar Wobbe index was confirmed. In particular the addiction of 10 % of hydrogen to pure methane doesn’t affect the behavior of the micro gas turbine either in terms of NO or CO emissions.

The influence of changes in fuel calorific value to combustion performance for Siemens SGT-300 dry low emission combustion system

The effect of changes in fuel calorific value on combustion was investigated on a single standard Siemens SGT-300 7.9MW dry low emission (DLE) combustor in a high pressure rig at actual engine operating conditions. The change in fuel calorific value was achieved by blending CO2 and/or N2 with Natural Gas. The lowest fuel calorific value was tested at a Wobbe Index (WI) of 23MJ/m3 which was associated with 35% CO2 (in volume) added to Natural Gas. The engine loads tested varied from 5% to full load. NOx and CO emissions were measured in addition to the frequency and amplitudes of pressure fluctuations and various temperatures. The impact of pilot split (ratio of pilot fuel to total fuel mass flow rate) and fuel composition on these was investigated. The results showed a noticeable benefit where the reduction in WI provided a reduction in NOx emissions. The amplitude of the pressure fluctuations was not an issue being controlled, where necessary, by pilot split. The test results showed that WI of 25MJ/m3 appeared critical to combustion performance compared to Natural Gas. Review of the literature and calculation of the flame properties attempted to provide explanations for the trends observed during testing.