Under Different Working Conditions Carbon Oxides and Nitrogen Oxides Emission of n-Butanol and LNG in Diesel Engine

. Through the establishment of covering substances such as CH 4 , C 4 H 10 O, nitride specific combustion reaction mechanism, carbon oxides and nitrogen oxides emissions can be simulated by CHEMKIN-PRO at the four fuel mixing ratios and same excess air coefficient, the Man 6S35ME-B9dual-stroke diesel engine was used as the experimental object. Changes in temperature, pressure, mole fraction of NO and mole fraction of CO 2 in the reactor were investigated at 1.5 ， and the influence factors of crank angle on pollutant emission of marine diesel engine under various operating conditions were studied. The simulation results show that with the loss of the diesel engine rotating speed, exhaust temperature and exhaust pressure significantly reduced. In the meantime, the mole-percent of NO and CO 2 decreased with the decrease of rotational speed. Compared with the rotational speed of 142 r/min, the molar mass of NO and CO 2 in exhaust gas decreased by 54.7% and 24.1% at 89.5 r/min, respectively.


Introduction
Shipping is the main way of global cargo transportation, and various ships bear 90% of the world's cargo transportation. [1]As the heart of the ship, the marine diesel engine provides the power source for the navigation of the ship.Its performance affects the operation of the ship, and the emission of various pollutants also has a decisive impact on the environment.On the one hand, the number of ships is large, and the energy consumed by diesel engines accounts for a large proportion of the world's total energy consumption. [2]specially in some developing countries, the great development in the economy infossil fuel resources will be consumed in only 65 more years.In addition the emission produced by the combustion of fossil fuels also contributes to the air pollution and global warming. [3]ince the beginning of the 21 st century, the energy crisis and environmental protection have prompted people to seek clean and efficient new energy, and also accelerated the research progress of using new fuel diesel engines. [4]here is a worldwide interest in sustainable energy sources based on biofuels. [5]The research shows that biodiesel is an ideal alternative energy source to petroleum diesel. [6]Improvements in the transportation sector's energy conversion efficiency and CO2 emissions can be realized with diesel engines using biodiesel fuel. [7]utanol is a bio-alcohol fuel that effectively reduces diesel engine smoke emission amount. [8]Compared with methanol and ethanol, n-butanol is better than diesel.The mutual solubility, complete mutual solubility without additives, and calorific value Higher, have better lubrication performance.Biodiesel and n-butanol are both contained Oxygen fuel has a great improvement effect on soot emission of diesel engine. [9]The study on dual fuel diesel engine has become a research hotspot in recent years for their good dynamic performance, economics and emission performance. [10]Compared with ethanol, n-butanol has less volatility and water absorption, which makes its transportation more convenient.In addition, n-butanol has the advantages of being easier to mix with practical fuels and can be directly used in traditional engines, so it is considered to be a very promising fuel in the future. [11]hipping emissions have become a catchword in the discussion about environmental protection.Carbon dioxide (CO2), being an important greenhouse gas (GHG) significantly present in Earth's atmosphere, has been increasing because of several anthropogenic activities leading to global warming. [12]NOx is a major cause of smog, ground level ozone and also a cause of acid rain.The development of improved NOx reduction technologies is therefore of critical importance to the global environment.Especially, Nitrogen oxide (NOx) emissions are of great concern because nitrogen removal is very difficult, and technologies related to reducing NOx emissions are still under development.According to Zelodvich combustion mechanism, the research purpose of this paper is to find the relationship between the of temperature, pressure, molar fraction CO2, molar fraction NOx for n-butanol and methane at different speeds.

Technical parameters and kinetics model
In this research, MAN 6S35ME-B9, Marine low speed two stroke direct injection diesel engine, is used as response model.This diesel engine has been widely studied due to its advantages, such as low rotational speed, low cost, light weight, and low power.The main parameters of engine are shown in Table 1.Setting: the rated speed is 142 r/min at 100% load, 129 r/min at 75% load, 112.8 r/min at 50% load and 89.5 r/min at 25% load.The opening and closing times of the sweep and exhaust ports are shown in Figure 1.The excess air factor is the ratio of the actual supply air quality to the theoretical supply air quality required for the perfect combustion of the fuel.The parameter plays a crucial role in quantifying the fuel-to-air ratio.In the engine combustion process, the combustion speed and the generation of burning products are also affected by the ratio of fuel to air.Oxygen is an accelerant in the combustion process of fuels.The higher the oxygen content, the easier it burns and the faster the flame spreads.If the proportion of fresh air is too small and the amount of oxygen is not enough, it will result in incomplete combustion of fuel and producing more polluting gases.Increasing the fresh air quality, the greater the probability of contact between fuel and oxygen, the easier the chemical reaction will take place.To enhance fuel combustion efficiency and minimize the generation of incomplete combustion byproducts like carbon deposition and CO, surplus coefficient of twostroke low-speed marine diesel engine is set to 1.5:1.0.
CHEMKIN-PRO softwares have been simulated nbutanol under various working conditions of dual-stroke diesel engine.The ratio of methane to n-butanol in the mixture was 7:3.The mixing ratio of the mixed fuel remains constant, and the diesel engine revolution was gradually increased to 89.5 r/min, 112.8 r/min, 129 r/min, 142 r/min, respectively.The relationship between pressure, temperature, CO2, NO, NO2 reaction mole fraction and crank angle were calculated.The formation mechanism of these reactions solely consists of elements C, H and O elements, so the reaction mechanism of NOx is added to the calculation simulation to facilitate the calculation, observation and analysis of the formation and transformation process of NOx.The main forms of nitrogen oxides produced during the combustion reaction are NO and NO2, in which NO accounts for the majority, and a part of NO is converted into NO2.
The chemical reacting equation for perfect combustion of n-butanol and methane gas is: (2) According to the equation, a fuel mixing ratio of 7 parts methane to 3 parts n-butanol ensures sufficient amounts of oxygen and nitrogen for complete combustion of both fuels at different speeds when the air coefficient is set at 1.5.According to the low calorific values of n-butanol and methane are 33.1 MJ/Kg and 55.65 MJ/Kg, respectively, it can be concluded that the consumptions of fuel, air and argon in different working conditions when the mixture ratio of methane and butanol is 7:3 in Table 2.

Result and Discussion
When the proportion of methane to n-butanol is 7:3, the excess air ratio is 1.5, and the rotating at 89.5 ~ 142 r/min, The combination of methane and n-butanol is employed as the fuel for HCCI combustion in a marine diesel engine with a two-stroke low-speed configuration.Fig. 2 shows the correlation between the reactor temperature and crank angle at the same ratio and different speeds of the mixed fuel.As the crank angle gradually increases, the temperature inside the reactor will slowly increase.Before the top dead center, the piston goes up, the gas in the cylinder is compressed, and the temperature in the cylinder is rising.In this process, there is no fuel in the cylinder, only the gas in the cylinder is compressed.The reason for the slow rise of temperature is as follows: initially, with the increase of temperature in the reactor, n-butanol in the reactor absorbs external energy to break the bond energy, and the molecular bonds C-C, C-O and C-H break to form alcohols and alkanes.The heat is absorbed by the reaction of n-butanol bond breaking, so the temperature in the reactor rises slowly.When the piston moves to the top dead center, the fuel is injected into the cylinder, and the fuel absorbs heat and vaporizes.Therefore, the temperature in the cylinder decreases briefly after the top dead center.The vaporized fuel reacts rapidly, and the temperature in the cylinder increases rapidly.The temperature within the reactor experiences a sudden increase to its maximum level, followed by a subsequent decrease until the point at which the exhaust port is opened.It is evident from the simulation findings that a continuous decrease in the speed of the diesel engine leads to a consistent reduction in both the maximum temperature and exhaust temperature within the cylinder.When the rotational speed reaches 142 r/min, the cylinder experiences a peak temperature of 2913.58K, and the emission temperature is 1465.13K.When the rotating at 129 r/min, the peak temperature in-cylinder is 2887.59K, and the emission temperature is 1424.12K.When the rotating at 112.8 r/min, the peak temperature in-cylinder is 2846.93K, and the emission temperature is 1352.894K.When the cylinder rotates at a speed of 89.5 r/min, it reaches a maximum temperature of 2700.87K, while the temperature at the exit is recorded as 1168.66K.When the rotational speed reaches 129 r/min, the cylinder experiences a maximum temperature of 2887.59K, while emitting heat at a temperature of 1424.12K.When the rotating at 112.8 r/min, the peak temperature in the cylinder is 2846.93K, and the discharge temperature is 1352.894K.When the rotational speed reaches 89.5 r/min, the temperature inside the cylinder reaches a peak of 2700.87K, while the temperature at the outlet stands at 1168.66 K. Fig. 3 shows that when the blending ratio of methane gas and butanol is 7:3, The coefficient of air excess is 1.5, while the revolution ranges from 89.5 ~ 142 r/min, a mixture of methane and butanol was application to HCCI combustion in a 2-stroke low-speed marine diesel engine.and the relationship between the pressure in the reactorand get the crank angle.It can be seen that as the crank angle increases, the pressure in the HCCI reactor enlarged gradually.When the piston reaches the top dead point, there is a sudden and significant rise in pressure within the reactor.It begins to decrease as the scavenging port opens.The main factor for the initially increased slowly in press is the upward moving of the piston and the compression of the gas mixtures.The temperature in the reactor rises and the pressure increases.When the piston reaches the highest point of its motion, there is an increase in temperature and pressure up to a specific level.The reactor's blended fuel undergoes combustion, resulting in the emission of a significant amount of thermal energy.The reactor experiences a significant increase in pressure, leading to the generation of a substantial amount of gas.As a result of the brief duration of the combustion process, there was a downward motion observed in the piston, leading to a subsequent decrease in pressure and temperature within the reactor.It is evident from the simulation results that there is a slight decrease in exhaust pressure following the peak combustion of the cylinder, and the decrease of the peak pressure in the cylinder can reduce the frequency of knock.When the speed is 142 r/min, the cylinder exhaust pressure is 7.92 atm.When the rotational speed is 129 r/min, the cylinder exhaust pressure is 7.87 atm.When the speed is 112.8 r/min, the exhaust pressure in the cylinder is 7.64 atm.When the rotating at 89.5 r/min, the venting pressure in-cylinder is 7.25 atm.In the event of an equivalent fuel quantity, decreasing the rotational speed of the diesel engine can effectively decrease both venting pressure and knock frequency.Under the condition that the mixture of methane and n-butanol fuel remains the same, different speeds have a certain effect on the NOx emissions generated by HCCI combustion of two-stroke low-speed marine diesel engines.The use of biodiesel in diesel engines will lead to an increase in NOx emissions.Because under this operating condition, the fuel supply is large, the injection pressure is high, the combustion temperature is high and the work is rough, resulting in an increase in NOx emissions.The biodiesel contains oxygen, which makes more oxygen in the combustion zone and promotes to the production of NOx.At the same time, the calorific value of biodiesel is low, which reduces the maximum combustion temperature and inhibits the production of NOx.This study will further reduce NO emissions by lowering speed.Figure 4 illustrates the correlation between the concentration of NO mole fraction in the reactor and the angle of rotation of the crankshaft, while maintaining a consistent mixture ratio but varying speeds.It is evident from the diagram that with the rise in temperature within the cylinder, NO gradually began to form, but the concentration was low.When the crank angle is about 3°, a large-scale oxidation reaction of N2 and O2 occurs in the reactor to promote combustion, and there was a sudden rise in the concentration of NO in the reactor.The emission of NO in close proximity to the highest point of compression exhibits a noticeable declining pattern as the maximum temperature during combustion within the cylinder decreases, and then for a period of time and slow decrease with the increase of crank Angle and remains the same, until the vent opens.
The reason for the decrease of NO molar mass in the later stage is that in the later stage of combustion, the natural gas is mainly burned in the cylinder, and the NO produced is less.A small part of NO produced in the cylinder decreases with the piston going down, and the fuel in the cylinder is reduced, which is oxidized by oxygen in the remaining air, so that the mass fraction of NO decreases.When the revolution is 89.5 r/min, the peak value of NO molar mass in the reactor is 7.52×10 -4 mol, and the NO molar mass in exhaust is 2.72×10 -5 mol.When the rotational velocity is 112.8 r/min, the peak value of NO molar mass in the reactor is 1.73×10 -3 mol, and the NO molar mass in exhaust is 4.37×10 -5 mol.When the revolution is 129 r/min, the NO molar mass peak in reactor is 2.15×10 -3 mol, and the NO molar mass is 5.26×10 -5 mol.When the revolution is 142 r/min, the NO molar mass peak in the reactor is 2.45×10 -3 mol, and the NO molar mass is 6.01×10 -5 mol.Compared with the speed of 142 r/min, the mass of the reactor decreased by 12.5% at 129 r/min.When the revolution of reactor was at 112.8 r/min, the mass decreased by 27.3%.At 89.5 r/min, the mass of the reactor decreased by 54.7%.It can be seen that the NO concentration in the tail gas increases with the number of revolutions.The results show that when the methane and n-butyl alcohol fuel mixture ratio must be, the cylinder experiences a reduction in both peak combustion temperature and emission temperature as the speed of the diesel engine decreases.The decrease of temperature has an inhibitory effect on the formation of NO, which leads to the decrease of NO emission.NO and NO2 are the main nitrogen oxides formed during the combustion of fuel, of which NO accounts for more than 95 %, and NO can be partially converted into NO2 after the formation of NO.
Fig. 4 The mole fraction of NO generated through combustion of a blended fuel at varying velocities.
Figure 5 is the main reaction path of NO to facilitate the calculation, observation and analysis of the formation and transformation process of NO.Can be seen from the diagram, can be directly involved in the reaction of the intermediate: HOCHO, HNO, NO2, CO2, NH2, N2, NNH, NO, H2O, HONO.The main sources of NO are the high temperature oxidation of nitrogen in the air and the reaction of nitrogen-containing compounds in the fuel with O2 to form NO. As depicted in Figure 6, the primary reaction equations associated with NO and the resulting yield of these reaction equations at a crank angle of 10° under 75% operational conditions.As evident from the provided reaction equations, NO involved in the reaction as a reactant and as a result.Fig. 6 Main reaction equation of NO and its absolute rate of production Fig. 7 shows the effect of speed 89.5 ~ 142 r/min on CO2 emission for a methane to n-butanol ratio of 7:3 and an air excess coefficient of 1.5.It is evident from the diagram that there is no substantial alteration in the reactor's CO2 mole fraction with an increase in crank Angle.When the piston reaches the highest point of its movement, there is a significant increase in CO2 levels within the reactor.After that, the molar mass of CO2 in the reactor decreases slightly, and Then increase slowly until the scavenging vent opens.Table 3 shows the molar mass of CO2 at rotational speeds of 89.5 ~ 142 r/min.When the revolution is 89.5 r/min, the peak value of CO2 molar mass in the reactor is 5.20×10 -2 mol, and the CO2 molar mass in exhaust is 5.74×10 -2 mol.When the rotational speed is 112.8 r/min, the peak value of CO2 molar mass in the reactor is 6.00×10 -2 mol, and the CO2 molar mass in exhaust is 6.85×10 -2 mol.When the revolution is 129 r/min, the CO2 molar mass peak in the reactor is 6.44×10 -2 mol, and the CO2 molar mass is 7.31×10 -2 mol.When the revolution is 142 r/min, the CO2 molar mass peak in the reactor is 6.62×10 -2 mol, and the CO2 molar mass is 7.56×10 -2 mol.Compared with the speed of 142 r/min, when the speed is 129 r/min, the peak value of CO2 molar mass in the reactor is reduced by 2.7%, and the CO2 in the tail gas is reduced by 3.3%.When the reactor speed is 112.8 r/min, the peak value of CO2 molar mass is reduced by 9.4%, and the CO2 in the exhaust gas is reduced by 9.4%.At 89.5 r/min, the peak value of CO2 molar mass in the reactor was reduced by 21.5%, and the CO2 in the tail gas was reduced by 24.1%.The reason that the molar mass of CO2 decreases and then increases is that the fuel will generate C when a series of cracking reactions occur.When the air coefficient exceeds 1.5, C first generates CO through oxidation reaction in the process of generating carbon dioxide, and then CO is oxidized to generate CO2.Because the fuel releases a lot of heat during the combustion reaction, and the chemical reaction time at this temperature is very short.Therefore, C will generate CO in a very short time, and CO will also generate CO2 in a very short time.It is evident from the diagram that as the revolution of the diesel engine decreases, there is a corresponding decrease in the molar mass of CO2 within the reactor.By reducing the speed, it becomes possible to effectively mitigate CO2 emissions.

Conclusion
When the CH4 and C4H10O ratio of 7:3, excess air coefficient is 1.5, the temperature reached its peak within the reactor, while the vent opening temperature showed a decrease in correlation with the reduction of speed.Compared to a rotational speed of 142 r/min, there is a decrease of 7.3% in the maximum temperature and a reduction of 20.24% in the exhaust temperature when operating at 89.5 r/min.As the rotational speed was reduced, there was a decrease in the mole fraction of NO observed at the exhaust port opening.Compared with the 142 r/min, 89.5 r/min when NO mole fraction was reduced by 54.7%.As the rotational speed decreases, the CO2 mole fraction at the outlet of the exhaust port decreases.Compared to a rotational speed of 142 r/min, there was a reduction of 24.1% in the molar fraction of CO2 at a lower rotational speed of 89.5 r/min.After examining the reaction path and mechanism of NO, it becomes evident that the decrease in NO mole fraction primarily arises from the transformation of a portion of NO into N2.Hence, the maximum temperature and exhaust temperature can be effectively decreased by lowering the speed of the diesel engine.The combustion characteristics remain unaffected by the proportional blending of C4H10O and CH4, leading to a subsequent decrease in pollution levels as both nitride and carbon emissions diminish with the reduction in rotational speed.
It is anticipated that in the future, nitrogen oxide emissions will be reduced in Marine dual-fuel internal combustion engines through the increased utilization of renewable energy sources like n-butanol.

Fig. 1 .
Fig. 1.Timing at which the sweep and exhaust ports.

Fig. 2 .
Fig. 2. In-cylinder temperature of mixed fuel combustion at different speeds.

Fig. 3 .
Fig. 3. In-cylinder pressure of mixed fuel combustion at different speed

2
NO H O +, NO is a product.Based on the overall production, the primary factor contributing to the reduction in NO mole fraction is attributed to the generation of N2.

Fig. 5
Fig.5 Main reaction pathway of NO when the crankshaft angle is 10°.

Fig. 7
Fig.7 The mole fraction of CO2 produced by mixed fuel combustion at different speeds.

Table 1 .
Basic technical parameters

Table 2 .
The quality of mixed fuel and air under different working conditions.

Table 3
The mole fraction of CO2 in cylinder and emission at different speed