Emissions of Compressed Natural Gas in a Wankel Rotary Engine Comparison with Gasoline Emissions

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Purpose

       Conventional piston engines running on gasoline pollute the atmosphere and further the current energy crisis. Modifying cars to run on the wankel rotary engine powered by Compressed Natural Gas (CNG) would serve to reduce the impact of cars on the environment as well as help to resolve the energy crisis. The purpose of this experiment is to convert a wankel engine to run on CNG and compare the emissions of the engine running on gasoline and CNG.

Hypothesis

       CNG is a cleaner burning fuel and I hypothesize that once the engine is set up to run on natural gas, the emissions will be much less than when the engine was running on 93 Octane Gasoline.

Background

       Conventional piston engines fueled by gasoline produce exhaust containing unburned hydrocarbons, carbon monoxide, and nitrogen oxides. Each of these gases is a pollutant, and has a negative impact on the environment. The adaptation of catalytic converters has reduced the emission of these gases, however researchers continue to look for ways to make automobiles greener in relation to the environment. While conventional piston engines use reciprocating pistons to generate power, the Wankel Rotary Engine uses less moving parts and a rotary design to typically produce higher output for similar displacement and physical size. The goal of this research is to combine rotary engine technology with natural gas as a fuel, to reduce automobile pollutant emissions, and minimize the effect on the environment

Procedure

       A Wankel engine from a 1970’s vintage snowmobile was mounted to workbench and run on conventional gasoline. The emissions were gathered (figure 3) every minute for five minutes and analyzed using Gas Phase Fourier Transform Infrared Spectroscopy (FTIR) (Figure 4) to determine the concentrations of unburned hydrocarbons, carbon dioxide, carbon monoxide, and nitrogen oxides. Results indicated that the content of the exhaust remained constant after 4 minutes of running time. The concentration of each pollutant was determined using a Beer’s law regression plot of a molecular vibration in the infrared spectrum that is specific to each component.

       The engine was then modified to run on compressed natural gas. However, because of difficulty in obtaining CNG, the natural gas was replaced with propane as it is easily obtainable, yet similar in structure to methane. The engine was set up to run at the same speed and use the same amount of oil, as the engine on gasoline. In order to ensure that the engine runs at the same speed as on gasoline, a computer fan was attached to the engine and the voltage was measured. When the voltage of the engine running on gasoline and on propane was the same, emissions were tested. To ensure that oil flow was the same as on gasoline, an oil pump was created. The engine was set up to run by removing the carburetor and injecting the oil and the gas directly into the engine intake. Emissions were once again gathered every minute for 5 minutes is the same as gasoline emissions were collected. Emissions were then analyzed in the same manner as before.

Results

       Initial results suggest that the concentration of emission gases stayed constant after four minutes of running start from a cold start. Therefore, emission gases will be analyzed at the fifth minute of running time because emission gases remain constant after this period. The regression curve of carbon dioxide (using CO2 to make the calibrations) showed that emissions decreased substantially. When the engine was running on gasoline, there was 13.72% of CO2 and this decreased to 1.41% when the engine ran on propane. This shows a considerable decrease in emissions that are known to pollute the environment. However, unburned hydrocarbon emissions had a different behavior. When the engine ran on gasoline, unburned hydrocarbon emissions (using butane to make the calibration) were 0.05% with the engine running on gasoline, but this increased to .72% when the engine ran on propane. This shows an increase in emissions that are also harmful to the environment. However, this increase is probably caused by problems in regulating the flow of propane into the engine.

       As time progressed, the flow of propane cooled the tank so much that the flow decreased. In order to ensure that the engine ran at a constant RPM, the flow valve to be opened more. The engine did run at constant speeds, but the lack of control of gas flow meant that there might have been too much gas entering the engine which probably flawed unburned hydrocarbon results. Although no calibration curve was created for carbon monoxide due to the difficulty of both creating or purchasing pure carbon monoxide. However, the peak area of carbon monoxide decreased when the engine ran on propane. This means that if a calibration curve had been created, there would have been a decrease in highly toxic CO emissions which would be very beneficial to the environment. CO emissions of the wankel running on propane are barely noticeable on the spectra (figure 8), but they are very clear when the engine ran on gasoline. Another calibration curve was created for nitrogen oxides (NOx) by mixing nitric acid with copped powder and collecting the emissions and analyzing them using FTIR spectroscopy. However, when the NOx spectra was compared to the spectra of the engine running both on propane and gasoline (Figure 9) there seemed no direct correlation between engine emissions and NOx. This means that there is no clearly identifiable NOx peak from the engine emissions. This lack of correlation shows that there is negligible NOx created when the engine ran on both gasoline and propane. Overall, there was a definite drop of CO2 emissions as well as CO emissions. There was an increase of unburned hydrocarbon which was probably created by the difficulty in regulating the flow of propane into the engine. Furthermore, there seemed to be negligible amounts of NOx in the engine running both on gasoline and propane. Overall, combining the two synergies of a wankel engine and CNG technology does create a clean and efficient engine.

       As time progressed, the flow of propane cooled the tank so much that the flow decreased. In order to ensure that the engine ran at a constant RPM, the flow valve to be opened more. The engine did run at constant speeds, but the lack of control of gas flow meant that there might have been too much gas entering the engine which probably flawed unburned hydrocarbon results. Although no calibration curve was created for carbon monoxide due to the difficulty of both creating or purchasing pure carbon monoxide. However, the peak area of carbon monoxide decreased when the engine ran on propane. This means that if a calibration curve had been created, there would have been a decrease in highly toxic CO emissions which would be very beneficial to the environment. CO emissions of the wankel running on propane are barely noticeable on the spectra (figure 8), but they are very clear when the engine ran on gasoline. Another calibration curve was created for nitrogen oxides (NOx) by mixing nitric acid with copped powder and collecting the emissions and analyzing them using FTIR spectroscopy. However, when the NOx spectra was compared to the spectra of the engine running both on propane and gasoline (Figure 9) there seemed no direct correlation between engine emissions and NOx. This means that there is no clearly identifiable NOx peak from the engine emissions. This lack of correlation shows that there is negligible NOx created when the engine ran on both gasoline and propane. Overall, there was a definite drop of CO2 emissions as well as CO emissions. There was an increase of unburned hydrocarbon which was probably created by the difficulty in regulating the flow of propane into the engine. Furthermore, there seemed to be negligible amounts of NOx in the engine running both on gasoline and propane. Overall, combining the two synergies of a wankel engine and CNG technology does create a clean and efficient engine.

Conclusions

• If an wankel engine is set up to run on propane, carbon dioxide and carbon monoxide emissions will decrease.
• If the wankel engine intake is tuned properly, unburned hydrocarbon emissions could decrease.
• Negligible nitrogen oxides were created with the engine running both on propane and gasoline.

Future Work

• Future work could consist of obtaining a side exhaust system and test the difference in emissions. A side exhaust system could make an exceptionally efficient and clean engine.
• Further research could also consist of combining Wankel and CNG synergies with other technologies such as the flywheel to make a truly efficient vehicle.