Chapter 3: Software Tool Based on Empirical Analysis of MicroElectroMechanical
3.2 Software implementation
3.2.2 Graphical User Interface (GUI)
Biodiesels are increasingly being used in ground transportation system. For this reason, most emission studies of biodiesel is focused on the internal combustion reciprocating engines such as compression ignition (CI) engine [73] or highly homogeneous compression ignition (HCCI) engine [74]. However, reports on the biodiesel emissions of NOx and CO from existing engines have been inconsistent. Some studies have shown that biodiesel reduces the emissions CO, UHC, PM emissions but increases NOx [75-77], while others have reported the decrease of NOx [78-80]. Such discrepancy in the literature could be attributed to the variation of parameters such as the engine models, injection timing or the quality of the biodiesel. Nevertheless, these results reveal the potential of biodiesel and provide the necessary insights to implement emission mitigating measures.
As mentioned previously, the use of biodiesel is not restricted only to diesel engines. There is growing interest in using biodiesel in gas turbine type engines for power generation. However, information related to biodiesel utilization in gas turbine engines remains relatively scarce. The emission results of biodiesel derived from internal combustion engines are not inferable to gas turbines due to the distinct difference in flame structure, i.e., compression type engine operates with an intermittent non-premixed reaction under extreme high pressure, whereas gas turbine combustor produces an overall lean, partially-premixed reaction with longer residence time for the droplet vaporisation process [81].
One of the advantages of the gas turbine is the greater flexibility in fuel choice with lesser fuel chemistry constraints. For example, the cetane number of a fuel is an important parameter for internal combustion engines but not for gas turbines. In recent years, several field tests have demonstrated the feasibility of using alternative fuels
Literature review on biodiesel emissions test that utilised a 40 MW, E class gas turbine, the NOx emission of rapeseed methyl esters was reported to be lower compared to diesel fuel [84]. The observed lower NOx
emission is due to the lower adiabatic flame temperature of biodiesel compared to diesel fuel, as explained by Glaude et al. [85] through a detailed calculation of the enthalpy and free energy of the mixtures. Higher adiabatic flame temperatures such as the case using diesel fuel, encourages the production of higher NOx through the mechanism of
“thermal NOx”. However, Ellis et al. [86] examined the emissions of soy, palm biodiesel and 20 % biodiesel blend with diesel volumetrically in a semi-closed cycle gas turbine.
The result showed almost similar emissions of NO and CO for all the fuels tested.
There have also been some biodiesel emission studies in a micro gas turbine combustor. Krishna [87] examined the emissions of soy biodiesel and blends of soy biodiesel with diesel fuel in a 30 kW microturbine (Capstone C30). The result showed that all the biodiesel blends including the neat soy biodiesel exhibited the reduction of CO and NO emissions compared to diesel fuel without any loss of thermal efficiency.
However, this result contradicts the more recent experiments that utilised the same 30 kW microturbine (Capstone C30) [81], where soy biodiesel was used and the NO emission was shown to be higher compared to diesel fuel. Variation of the air-liquid mass ratio (ALR) parameter shows significant influence on the emissions performance.
NO emissions for biodiesel were found to decrease with an increasing ALR. The experiment showed that optimized NO and CO emissions can be achieved with the modification of the operating conditions or injector.
Nascimento et al. [88] investigated the thermal and emission performance of castor biodiesel and biodiesel blends with diesel in a 30 kW diesel microturbine engine.
The thermal performance showed that the use of pure biodiesel fuel resulted in a higher fuel specific consumption compared to diesel due to the lower heating value. The emission result showed an increase of CO and a decrease of NO emissions compared to diesel fuel. Comparison of the emissions performance of biodiesel and Jet-A1 fuel was performed by Habib et al. [89] in a 30 kW gas turbine engine. The fuels tested were biodiesel derived from soy, canola, rapeseed, animal-based and blends of biodiesel with Jet A fuel. The results indicated that although the turbine inlet and engine exhaust gas temperature did not show significant changes with the fuel type, the CO and NO
Literature review on biodiesel emissions emission concentration decreased when biodiesels were used. Pure biodiesel was also found to show higher thermal efficiencies than Jet A and biodiesel blends.
Ramotowski et al. [90] investigated the emissions performance of palm and soy biodiesel using a gas turbine engine hardware (Solar Turbines Centaur 50 fuel nozzle).
The combustor inlet air was preheated to 625 K and the pressure of the combustor was maintained at atmospheric conditions. The NO and CO emissions level of the biodiesels was lower than from diesel fuel. The higher NO emissions of diesel is due to the presence of fuel-bound nitrogen. Biodiesel contains no fuel-bound nitrogen and hence the NO emission level of biodiesel is similar to natural gas and Fisher-Tropsch fuel (S-8) [90].
Sequera et al. [91] utilised a generic gas turbine type combustor to establish a swirling spray flame for the investigations of biodiesel emissions. The fuels tested were diesel, soy methyl ester, soy ethyl ester and bio-oil pyrolised from hardwood. The results demonstrated that lower emissions of NOx and CO were obtained for the biodiesel-blended fuels at the operating conditions when all the fuel flow rates are kept constant. An increase of atomizing air through the atomizer resulted in the reduction of emissions. A similar trend was also observed in the experiments conducted by Panchasara et al. [92] using the same setup. They reported that an increase of 67 % in the atomizing air flow rate could reduce the emissions of CO and NO by a factor of 5 and 10 respectively. The reduction of the NO emissions is associated with the lower flame temperature as a result of the increase of atomizing air.
Hashimoto et al. [93] investigated the emissions of palm biodiesel relative to diesel in a gas turbine type burner at atmospheric pressure. The atomizer used in the burner was a pressure-swirl type. It was reported that NO emissions for palm biodiesel were consistently lower compared to diesel fuel when plotted as a function of excess air ratio, droplet SMD, atomizing air pressure and viscosity. The measured CO and unburned hydrocarbons were within the range of 2 ppm.
From the review, most studies show that biodiesel produces lower NO and CO emissions when operating under the gas turbine conditions. The presence of oxygen in biofuel molecules contributes to locally leaner combustion, increased fuel consumption and thermal efficiency as observed in some experiments. The following section describes the mechanism of pollutant formation.
Formation of pollutants