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A Numerical Study on Effect of Ignition Timing and Mixing Ratio of Natural Gas Spark Ignition Engine

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A numerical study of the effect of ignition timing and mixture ratio of a spark ignition natural gas engine. A numerical study of the effect of ignition timing and mixture ratio of a spark ignition natural gas engine. A numerical study of the effect of ignition timing and mixture ratio of a spark ignition natural gas engine on engine performance.

Comparative results are given for different ignition timings and different mixture ratios, revealing the effect of ignition timing and mixture ratio on engine performance and exhaust emissions.

INTRODUCTION 1 Background

  • Engine knock
  • Natural gas as an alternative for engine
  • Problem statement
  • Objective of the study
  • Scope of the study
  • Thesis organizing

Global natural gas production and projection by region (Source: Exxon Energy Outlook- 2015 & BP Energy Outlook-2016). Properties of Natural Gas and Diesel (Alternative Fuels Data Center, 2004) Diesel Conventional Compressed Natural Gas Property.

Figure 1-1. 1 Yearly Production as the percentage of Proved Reserves and Proved Reserves of Global  Natural Gas by year end 2014 (Source: BP Statistical Review of World Energy 2015)
Figure 1-1. 1 Yearly Production as the percentage of Proved Reserves and Proved Reserves of Global Natural Gas by year end 2014 (Source: BP Statistical Review of World Energy 2015)

LITERATURE REVIEW 1 Introduction

Engine classifications for automotive purpose .1 SI engine

  • CI engine

However, since natural gas when injected displaces some of the air in the intake manifold, a reduction in volumetric efficiency occurs, which in turn leads to a proportional reduction in power. Natural gas direct injection in SI (and CI) engines requires the development of special high-pressure gas injectors that are currently not available on the open market. In addition, natural gas direct injection has been shown to extend the lean operating limit of normal engine operation compared to port fuel injection [14].

Most of the dual-fuel engine studies to date have been conducted in conventional diesel engines modified to feed natural gas into the combustion chamber through the intake manifold, while retaining the original injector in the fuel injection cylinder. As with port-injected SI engines, introducing natural gas through the intake manifold reduces volumetric efficiency, and thus potential power (c.f. natural gas direct injection dual-fuel engines maintain power and thermal efficiency compared to conventional non-dual-fuel diesel engines). engines [16].

Further improvements to CI dual-fuel engines with natural gas direct injection can be achieved by varying the injection pressure of the natural gas jet and diesel pilot fuel. Increasing the injection pressure of both diesel pilot fuel and natural gas injection (from 21 MPa to 30 MPa) results in a shorter pilot fuel ignition delay [17] due to faster mixing between the pilot fuel and air during the ignition delay. period. These emission trends result in better mixing rates between the pilot fuel, natural gas and air in addition to faster rates of combustion progression.

Review of previous study on engines with natural gas

Peak cylinder pressure (PCP) and indicated thermal efficiency (ITE) initially increase due to higher boost pressure with increasing EGR rate. At cylinder pressure, temperature and heat release rate increase with earlier spark timing, but the rate of increase decreases with higher engine speeds. NOx emissions also increase with earlier spark timing due to higher in-cylinder temperature.

The purpose of this study is to optimize the ignition timing best suited for idling in normal operating mode (700-850 rpm) and cold start rpm). A few anomalies were found in the result, but overall the 25oBTDC ignition timing is better than the 20oBTDC in terms of fuel consumption and exhaust emissions. Javad Zareei et al [22] were to investigate the effect of ignition timing and hydrogen content on engine performance and exhaust emissions.

The results showed that when hydrogen volume fraction was increased from 0 to 50% at 20 bar injection pressure and at the ignition time from 19 to 28 °CA BTDC, a good stratified effect was obtained. In addition, the advance of the ignition timing caused NOx, HC and CO emissions to decrease, but with the increase of hydrogen fraction in the mixture of fuel, HC and CO decreased. Additionally, this study concluded that the 30% blends of hydrogen and 21° BTDC ignition timing can optimize engine performance and emissions without any engine modification.

Figure 2-3. NOx concentration [19]
Figure 2-3. NOx concentration [19]

Summary

In some literature, the induction method used prevents the formation of a mixture of air with a mixture of natural gas in the intake manifold (so that the natural gas supply is separated from the incoming air until very close to the intake valve). Failure of the pilot fuel to ignite the entire charge of natural gas and air at low and intermediate loads (due to low charge temperatures) results in lower thermal efficiencies. In order to take full advantage of SI and CI engines running on natural gas, extensive optimization of the performance and emissions of both engine types is required.

In dual fuel CI engines, natural gas can be used in smaller amounts compared to the pilot fuel at lower loads to reduce HC and CO emissions (ie the pilot fuel will provide more than 50% of the total fuel energy input). High-pressure pilot fuel injection (on the order of 100 MPa) can provide multiple ignition points that are more widely distributed throughout the natural gas air charge. An increased number of diesel injector holes smaller than standard allows better atomization and mixing of the pilot fuel with the natural gas [24,25].

Since natural gas is not a renewable fuel, renewable sources of methane are needed to ensure its long-term use. This biogas can be used quite well in natural gas engines; however, this would result in reduced power and efficiency caused by contaminants in the biogas, such as CO2 and sulfur dioxide (SO2). In general, natural gas engines can complement the existing engine portfolio and contribute to conserving the limited supply of crude oil.

CALCULATION METHOD 1 Calculation methods

  • CHEMKIN overview
  • The process of the SI engine model calculation
  • Engine specifications
  • Determination of low temperature reaction (LTR), high temperature reaction (HTR), CA50 and ignition delay
  • Determination of knocking and misfire
  • Combustion analysis
  • Fuel properties
  • Validation of simulation model

In Figure, start and end time of both low temperature response (LTR) and high temperature response (HTR) and 50% focal point of total heat release are shown. It can correspondingly increase the heat release rate [J/ms] if the input calorie is increased. To prescribe the SI combustion without preventing knocking in the operational region, the simplest basic criterion is to set the limits of the maximum pressure rise rate.

Although the limits of the maximum pressure rise rate are a useful criterion to set, but not always applicable standards. Pmax must be given as kPa, whereby Eq. (3-1) gives the listening power in kW/m2. The speed of sound comes in through the square root expression, and must be in m/s.) The use of a time-based pressure rise for the calculation of knock/knock is justified by the fact that the acoustic time scales are independent of the engine speed. This data can be used to obtain information about the combustion process such as the HRR and burn duration.

COV represents the standard deviation of the data as a percentage of its mean. The confidence of the simulated model was evaluated from the comparison between the experimental results and the simulated results. Before using the simulated model to estimate the effect of ignition timing, this model was calibrated and validated.

Figure 3-2. Algorithm flow diagram for SI engine
Figure 3-2. Algorithm flow diagram for SI engine

RESULT AND DISCUSSION

Effect of ignition timing and mixing ratio on engine performance of engine fueled with natural gas

  • Effect of ignition timing and mixing ratio on IMEP
  • Effect of ignition timing and mixing ratio on brake torque
  • Effect of ignition timing and mixing ratio on power
  • Effect of ignition timing and mixing ratio on ignition delay
  • Effect of ignition timing and mixing ratio on thermal efficiency
  • Effect of ignition timing and mixing ratio on brake specific fuel consumption

The engine's maximum IMEP was 6.897 bar with 20 percent propane and at 39 spark degrees with advanced ignition timing. The effect of spark ignition timing on braking torque for each percentage of propane when mixing methane with propane is shown in Figure 4-4. The engine's peak brake torque was 101.0898 Nm at 20 percent propane and at 39 spark degrees with advanced ignition timing.

The effect of spark ignition time on power for each percentage of propane when mixing methane with propane is shown in Figure 4-5. The maximum ignition delay was 10 percent propane in the blends and at 42 degree spark advanced ignition timing. Minimal ignition delay with pure methane and advanced ignition timing at 27 degrees spark.

Maximum thermal efficiency was 36.84% with 5 percent propane and at 39 degrees spark advanced ignition timing. Minimum thermal efficiency was 32.53% with 20 percent propane and at 21 spark advanced ignition timing. The effect of spark ignition timing on thermal efficiency for each percent of propane when mixing methane with propane was shown in Figure 4-8.

Figure 4-1. Effect of ignition timing and mixing ratio on peak temperature
Figure 4-1. Effect of ignition timing and mixing ratio on peak temperature

Effect of ignition timing and mixing ratio on emissions characteristics of engine fueled with natural gas

  • Effect of ignition timing and mixing ratio on CO
  • Effect of ignition timing and mixing ratio on NOx

In addition, the BSFC tends to decrease with increasing spark advanced ignition timing from 21 to 39 degrees, but tends to increase from 42 to 48 degrees. The effect of spark ignition timing on CO emissions for each percent of propane when mixing methane with propane is shown in Figure 4-19. The value of CO emissions increases as the percentage of propane in the mixture increases.

It can be explained that increasing the percentage of propane in the mixture will lead to an increase in BSFC, thereby reducing the fuel from completely burning with oxygen, leading to an increase in CO emissions in the exhaust gas. Furthermore, as the advanced ignition timing decreases, CO emissions will decrease because the fuel does not have enough time to react with the oxygen. The effect of spark ignition timing on the NOx emissions for each percent propane when mixing methane with propane is shown in Figure 4-30.

The value of NOx emissions increases with increasing percentage of propane in the mixture. We can explain that an increase in the percentage of propane in the mixture will cause an increase in the temperature in the cylinder, which will intensify the reaction between nitrogen and oxygen, and as a result, the amount of NOx emissions in the combustion chamber will increase. In addition, as the ignition advance timing increases, NOx emissions will increase because an increase in ignition advance timing will cause an increase in combustion chamber temperature and pressure, resulting in an increase in NOx emissions.

Figure 4-9. CO emissions with ignition timing 21 deg
Figure 4-9. CO emissions with ignition timing 21 deg

SUMMARY AND CONCLUSION

Crookes, "Natural Gas Powered Spark Ignition (SI) and Compression Ignition (CI) Engine Performance and Emissions", Progress in Energy and Combustion Science. Effect of the compression ratio on the performance and combustion of a natural gas direct injection engine. The effects of high pressure injection on a compression ignition, direct injection of a natural gas engine.

수치

Figure 1-1. 1 Yearly Production as the percentage of Proved Reserves and Proved Reserves of Global  Natural Gas by year end 2014 (Source: BP Statistical Review of World Energy 2015)
Figure 1-3. Global natural gas production and projection by region (Source: Exxon Energy Outlook- Outlook-2015 & BP Energy Outlook-2016)
Figure 1-4. World unconventional gas phenomenon (Source: World Energy Council 2016)  Key growth factors in the demand for gas which initially was considered a by-product of oil  production,  were  its  environmental  credentials  (reducing  CO2  emissions)
Figure 1-5. Natural gas consumption by region & sector, BCM (Source: IHS CERA, LUKOIL  Estimates)
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