Effects of Emissions from Unburned Hydrocarbons under Cold Start - Term Paper Example

Effects of Emissions from Unburned Hydrocarbons under Cold Start Emissions from unburned hydrocarbons under cold start is a serious problem in the automotive industry that normally occurs in the initial few minutes of starting an engine when it still cold and has not achieved its optimal operating temperature, thereby resulting in inefficient and incomplete combustion. Combustions are initiated to start an engine although it is only possible with an appropriate air-fuel mixing rate. While a number of previous studies have primarily focused on the phenomenon of the extra emissions related to the conditions of cold start, little is known about the, magnitude of its potential effects. The present research seeks to critically investigate the potential effects of emissions from unburned hydrocarbons under cold start. Effects of Emissions from Unburned Hydrocarbons under Cold Start Introduction Emissions from unburned hydrocarbons under cold start are a serious problem in many diesel and gasoline automotive engines that is generally characterized by generation excessive extra emissions of pollutants. The problem particularly occurs in the initial few minutes of starting an engine when it still cold and has not achieved its optimal operating temperature, thereby resulting in inefficient and incomplete combustion. A cold start is common, as weather conditions in most climates will naturally be at a lower temperature than the typical operating temperatures of an engine. Additionally, extra emissions related to cold start may also occur when one ignites the engine of an abandoned or inactive vehicle for a significant amount of time (Raja and Arasu, 2014). While a number of previous studies have focused on the phenomenon of the extra emissions related to the conditions of cold start, little is known about the, magnitude of its potential effects. In the event of cold start, the engine compression is higher as the lack of heat makes ignition more difficult. Secondly the low temperatures cause engine oil to become more viscous, making it difficult to circulate. Similarly, the air becomes denser and affects the air-fuel ratio, which in turn affects the flammability of the mixture. Subsequently, in diesel engines combustion takes place compared to petrol engines where spark plug performs this combustion at high temperature and pressure. It is hard to get that high temperature and proper ignition point even with the enriched fuel mixture in cold weather. This paper critically investigates the potential effects of emissions from unburned hydrocarbons under cold start. Statement of the Problem Cold start is an automotive term implying the tendency to start vehicle’s engines when it is cold in relation to the preferably normal engine temperatures. Cold start is therefore due to cold weather. Recent statistics suggest that cold-start may result in up to 43 times higher emissions as compared to starting under ordinary operating temperatures (Hilliard and Springer, 2013). It is an important source of some of the major air pollutants some of which include unburnt hydrocarbons (HC), oxides of nitrogen(NOx), carbon monoxide(CO) and particulate matter among others. In addition, according to Faiz et al (2006), unburned hydrocarbons are also health hazards which make it vital to solve the problem of cold starting as an onset move to mitigate emissions of unburned hydrocarbons. The problem is usually evident in the initial few minutes of starting an engine when it still cold and has not achieved its optimal operating temperature, thereby resulting in inefficient and incomplete combustion. Generally, the rate depends on the temperature and fuel since they have an influence on vaporization. Vaporization of fuel is hard to propagate and start combustion mostly in the area where air and fuel mix as the temperature gets colder, more difficult if the temperature is lower and, as a result, it is hard to start combustion and propagate a flame. For example, when air becomes denser and affects the air-fuel ratio, which in turn affects the flammability of the mixture. Subsequently, in diesel engines combustion takes place compared to petrol engines where spark plug performs this combustion at high temperature and pressure. It is hard to get that high temperature and proper ignition point even with the enriched fuel mixture in cold weather. Consequently, to solve the cold start problems, a little fuel is injected to ensure that there is enough fuel mixed with the air. However, the major setback of injection is an increase of pollutant emissions. Current Understanding Unburned hydrocarbons under cold starting have various effects health-wise and environmentally. The emergence of global climate change is as a result of cold starting among other sources unburned hydrocarbon emissions in the atmosphere such as industries and deforestation. Additionally, emission of unburned hydrocarbons may result to the invisible atmosphere which in most cases is the reason behind accidents. Unburned hydrocarbons are also health hazards which makes it vital to solve the problem of cold starting as an onset move to mitigate emissions of unburned hydrocarbons (Faiz et al, 2006). This situation, currently resulting to pollution, global warming and increased atmospheric conditions variations is very common. The commonplace nature of cold start is as a result of weather conditions in most areas which naturally lower the temperatures in relation to the typically preferable operating temperatures of engines (Sarshar, 2008). Cold start can also refer to starting engines which have been inactive, abandoned or neglected for significant durations such as months, years or decades. Cold starts key in some difficulty than while starting a vehicle which has been used recently. This process thus results to incomplete combustion of the hydrocarbons. Reasons for cold start include; increased viscosity of the engine oil which makes it more difficult to circulate, denser nature of air and the higher levels of engine compression. According to Hilliard and Springer (2013), spark-ignited engine essentially leaves no hydrocarbons in the residual burned gasses. The authors argue that the primary source of hydrocarbons found in the exhaust result from the section of the fuel-air intake charge trapped during the compression stroke. Additionally, the hydrocarbons are found inside the cylinder into which the main combustion flame cannot enter. The authors pointed out that the cold walls of the combustion chamber produce the thin layer of the unburned air-fuel mixture. The two sources of unburned hydrocarbons find their way into the gasses during the exhaust stroke and the later portion of the power stroke. The gasses leave the cylinder during the exhaust stroke (pg. 61). Consequently, in the exhaust port and exhaust manifold, a portion of the residual hydrocarbons are combusted to CO or CO2. The remainder leaves the exhaust manifold to give rise to hydrocarbon emissions of the engine. A larger percentage of these hydrocarbons are unburned fuel. Control to this hydrocarbon source is crucial in reducing hydrocarbon emissions. However, the hydrocarbon emissions are low from the diesel engines where there is no injection of fuel until the piston approaches the top of the compression stroke. Similarly, unburned hydrocarbons emissions result when fuel molecules in the engine do not burn or burn partially. Consequently, this leads to ignition misfires, low compression, excessively rich mixtures, or oil leakages past the valves or rings. Equally, it is essential to note that in the first minutes of engine operation, when the coolant temperatures are low and the engine block, incomplete combustion results in significantly higher emissions. The hydrocarbons once released from to the atmosphere, react in the presence of sunlight and nitrogen oxides to form ground-level ozone (O3), a major component of smog. In addition, unburned hydrocarbons forms part of a broader category known as Volatile Organic Compounds (VOCs), which can cause headaches, nausea, and kidney and liver damage. However due to the rising concern of pollutants in the air, there are various ways proposed to reduce the emissions. Solutions to the Problem There are a diverse number of possible solutions many of which have been previously used to solve the problem, One of the ways is through which the problem of the emissions from unburned hydrocarbons under cold start can be addressed is development of a three-way catalyst. A three-way catalytic converter is a device found in the vehicle after treatment systems to reduce harmful air pollutants. The catalysts primary task is to convert three harmful pollutants into less harmful H2O, N2, and CO2. The efficiency of a catalytic converter varies with temperature and therefore during cold start, the catalyst bypasses harmful emissions. However to compensate for the catalysts ineffectiveness, several proposed methods. One common method is using a hydrocarbon absorber that traps hydrocarbons until the catalyst reaches light-off temperature. Another potential solution to cold starting is the use of electric starter motors may be some of the ideal automotive moves to improve the chances of successful ignition. Diesel engines should make use of glow plugs. These plugs reduce incomplete combustion through heating of the engine blocks prior to ignition. Additionally, the glow plugs will improve the conditions inside the engines. This engineering model has been adopted by various manufacturers such as in the Mazda RX-7 model. The Mazda RX-7 model have been modified to reduce cold starting through the incorporation of block heater which heats the whole engine block before ignition thus reducing the problem of cold starting. Another method is the use of a close-coupled catalyst. The design involves placing the catalyst near or within the exhaust manifold. The last method is using an electrically heated catalyst (EHC). An EHC works by sending an electrical current through a foil structure that transfers heat to gasses within the EHC. The hot gasses flow to heat the main catalyst through the exhaust. There are two categories of proposed strategies to reduce hydrocarbon emissions: one where the hardware components of the vehicle are physically modified and the other in which there ae proposed changes to the setting of the engine operation, in particular, the combustion parameters. In the first group, a catalyst is presented to achieve faster light off. The problem generally occurs in the initial few minutes of starting an engine when it still cold and has not achieved its optimal operating temperature, thereby resulting in inefficient and incomplete combustion Secondly standards are achieved by using new technologies: high-velocity air and high swirl combustion, great low heat mass substrate catalyst, two-stage high-efficiency hydrocarbons trap catalyst system and triple sensor highly accurate air-fuel ratio control system. In the second group, there is the use of already existing components of the vehicle to improve the performance of the system. For example, a limit control is used to reduce hydrocarbons. The increase in exhaust temperatures could by maintaining high idle speed with a high value of ignition retard. Similarly, a strategy combining retarded spark timing with high engine speed is used. Key developments and Future Directions Due to new technologies e.g. improved engine control algorithms and the catalyst, there is a considerable reduction in cold-start emissions over the last 10 years. For normal stop times of 0.5-4 hours, the average cold-start emissions of new vehicles are below the mean of the additional relative emissions of 10-year-old cars. Besides improvements in catalytic converter design, thermal energy storage system and optimization of operating variables, researchers are attempting to reduce cold start emissions by fuel modifications and heated air and fuel injection. The use of heated intake air and ethanol in substitution to the conventional system produced significant reductions in raw exhaust hydrocarbons emissions (Raja & Arasu, 2014, p. 1). Similarly, latest vehicles are equipped with internal combustion engines due to catalyst improvements and electronic mixture control. Then internal combustion engine is the most significant part of the total emissions. While PM 10 and PM 2.5 emissions from the internal combustion engines are an area of concern, vehicle brakes articulately generates more PM 10 on average wear and tear emissions. In comparisons with cold starting, in the warmer summer months, there is decline in both starting and running PM emissions; through in these months, tire and brakes-related emissions are actually recorded to be on the increase (Sarshar, 2008). Simulations performed using the EPA’s moves system enlightens on the geographical location, CH4, N2O and VOC constituents. Through these impacts are minimally as a result of cold starting, this environmental degradation-oriented process can be easily mitigated. The mitigations measures for cold starting include the use of other potential sources of vehicle power such as electricity. This could additionally have major positive and negative impacts for the future transportation. Health and environmental benefit issues are also in line with this topic of study. Cold starting is hazardous thus various health-based policies should be formulated to ensure an alternative and safe source of vehicle energy use. Lastly, the basic technological advancement skills knowledge is inevitable while tackling the topic on unburned hydrocarbons. These technological issues include ICT for sustainability effects and the hybrid electrical vehicles manufacturing proposals. Conclusion In conclusion, the extra emissions of unburned hydrocarbons emissions result when fuel molecules in the engine do not burn or burn partially. Unburned hydrocarbons forms part of a broader category known as Volatile Organic Compounds (VOCs). However due to the rising concern of pollutants in the air, some of the ways proposed to reduce the emissions is through new technologies e.g. the catalyst and improved engine control algorithms. As a result, cold start emissions have been considerably reduced over the last 10 years. References Hilliard, J. C., & Springer, G. S. (2013). Fuel Economy: in Road Vehicles Powered by Spark Ignition Engines. Springer Science & Business Media. Retrieved on December 9, 2015 from https://books.google.co.ke/books?id=2MMAq5mIlE4C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false Faiz, A., Weaver, C. S., Walsh, M. P., & Gautam, S. P. (2006). Air pollution from motor vehicles; standards and technologies for controlling emissions. Washington, D.C: The World Bank. http://www-wds.worldbank.org/external/default/WDSContentServer/WDSP/IB/1996/11/01/000009265_3970311120405/Rendered/PDF/multi_page.pdf Raja, A. S., Arasu, A. V. (2014). Control of cold start hydrocarbon emissions of motor bike engine by gasoline-ethanol blends and intake air heating. Journal of Mechanical Science and Technology, 28(4), 1567–1573. http://doi.org/10.1007/s12206-014-0305-4. Reiter, M. The Problem Of Cold Starts: 2 A Closer Look At Mobile Source. Retrieved on December 9, 2015 from http://www.caee.utexas.edu/prof/kockelman/public_html/TRB15coldstarts.pdf Read More