Exhaust Emission in IC Engines: A Review[edit]

Abstract[edit]

There has been a great concern, in recent years, that the IC Engines are responsible for too much atmospheric pollution, which is detrimental to human health & environment. Thus concerned efforts are being made to reduce the responsible pollutants emitted from the exhaust system without sacrificing power & fuel consumption. Emission of these harmful chemicals from IC engines is mainly due to incomplete combustion. The major pollutants emitted from the exhaust due to incomplete combustion are Carbon monoxide (CO), Unburnt hydrocarbons(HC), Nitrogen Oxides(NO_X) and other emissions are Sulphur oxides(SO_X), acetylene, aldehydes, particulate smog, soot particles and lead. However, if the combustion is complete only products being expelled from the exhaust would be water vapor which is harmless, and carbon dioxide, which is not directly harmful to humans.

This paper contains the recent research carried out regarding exhaust emission in IC engines. The researchers incorporated suitable methods for increasing the performance and to reduce the exhaust emission in IC engines.

Introduction[edit]

The major pollutants emitted by the diesel engines are unburned hydrocarbon (HC), carbon monoxide (CO), oxides of nitrogen (NOx), particulate matter (PM), sulphur oxides (SO_x) and lead. These pollutants can cause health problems to human beings and will have an impact on the environment. Therefore, the researchers are intended to find out the viable substitute alternate fuel for diesel and control of pollutants from compression ignition (CI) engines. The biodiesel can be used as alternate for diesel, which is a non fossil fuel, easily available and cheaper. The main drawbacks of biodiesel operated CI engine are reduced performance and increased NOx emission. In order to improve the performance and to reduce exhaust emissions, suitable methods have to be incorporated. A detailed study has been carried out with the operating parameters and catalytic converter in biodiesel operated engine, so that its performance can be improved and exhaust emissions can be reduced. [1]

Controlled auto ignition (CAI) or, also known homogenous compressed ignition, is an advanced combustion technology allowing a lower NOx emission and fuel consumption that can relieve the energy demand based on petroleum. The objective of this study is to determine the effects of spark ignition (SI), spark assist controlled auto ignition (SI-CAI) and pure CAI combustion modes on the performance and emissions in a modified IC engine. The results showed that CAI combustion mode produced lower NOx emissions, although it resulted in higher CO and HC emission than those under SI and SI-CAI combustion modes. [2]

Vehicles are the main sources for environmental pollution especially those associated with diesel engines. It is very urgent to find alternative fuel for vehicles. Biofuel is an alternative for vehicles which have potential to reduce engine emissions and maintain the air quality better. In recent years, worldwide biofuel production and use raised drastically. Some developed countries have put their target and mandate to use biofuel. The aim of this review is to discuss the impact of biofuel on diesel engines emission. From this review it is found that biofuel significantly reduces engine emissions and it has potential to reduce more than 80% green house gas emission. [3]

The objective of this paper is to investigate the thermal performance, exhaust emissions and combustion behaviour of small capacity CI engine using varying energy fractions of ethanol. Significant reductions have been observed for CO₂ (carbon-di-oxide), NOx (oxides of nitrogen) and smoke with the use of ethanol in CI engine. CO (carbon mono-oxide) and HC (hydrocarbons) increased with the increase of ethanol energy fractions. [4]

A low-cost exhaust gas after treatment system called water-scrubbing is attempted in this paper. An emission treatment setup is fabricated & is installed in the exhaust of the engine. This takes the exhaust gas and sprays water in the exhaust and passes it through the chamber containing silica gel. The exhaust gas after treatment system helps to reduce emission of NOx, CO and Particulate matter. The performance of the engine has also been monitored to determine whether the engine has any decrease in performance when the setup is used and it is found that there is no change in the engine performance. [5]

In order to improve IC engine energy utilization efficiency, an open steam power cycle is used for IC engine exhaust gas energy recovery. The bottom cycle concept is designed on a four-cylinder naturally aspirated IC engine: with three cylinders taken as ignition cylinder, the last one is used for steam expansion cylinder; IC engine exhaust pipe is coupled with a Rankine steam cycle system which uses the high temperature exhaust gas to generate steam; then, the steam is injected into steam expansion cylinder and expands in the cylinder. In this way, the Otto cycle (or diesel cycle) of traditional IC engine and the steam expansion cycle (open Rankine cycle) are coupled on IC engine. The research results shows that the recovery efficiency of exhaust gas energy is mainly limited by exhaust gas temperature. The maximum bottom cycle power can reach 19.2 kW and IC engine thermal efficiency can be improved by 6.3% at 6000 r/min.[6]

Several methods for waste thermal energy recovery from internal combustion engine (ICE) have been studied by using supercharger or turbocharger or combined. This study presents an innovative approach on power generation from waste of IC engine based on coolant and exhaust. The waste energy harvesting system of coolant is used to supply hot air at temperatures in the range of 60–70℃ directly into the engine cylinder, which would be useful to vaporize the fuel into the cylinder. The result shows that specific fuel consumption of engine has improved by 3% due to reduction of HC formation into the engine combustion chamber causes significantly improved the emission.[7]

Exhaust gas recirculation (EGR) is a commonly recognized primary technique for reducing NOx emissions in IC engines. However, the application of EGR in diesel engines is associated with an increase in smoke emissions and a reduction in thermal efficiency. In this work, empirical investigations and parametric analyses are carried out to assess the impact of EGR in attaining ultra-low NOx emissions while minimizing the smoke and increasing efficiency. Two fuel injection strategies are studied, namely diesel-only injection and dual-fuel injection. In the dual-fuel strategy, a high volatility liquid fuel is injected into the intake ports, and a diesel fuel is injected directly into the cylinder. The results suggest that the reduction in NOx can be directly correlated with the intake dilution caused by EGR. [8]

A low-cost exhaust gas after treatment system called water-scrubbing is attempted in this paper. This system takes the exhaust gas and sprays water in the exhaust and passes it through the chamber containing silica gel. An attempt is made to investigate experimentally the performance and emission characteristics of a direct injection (DI) diesel engine, with and without water injection at the exhaust using diesel fuel (DF). The exhaust gas after treatment system helps to reduce NOx, CO and Particulate matter.[9]

The aim of this review paper is to discuss the effect of mixed blends of biodiesel alcohol and diesel on engine performance and emission parameters of a diesel engine. Most of the researchers reported that adding ethanol into biodiesel-diesel blend in diesel engines significantly reduce HC, PM, NOx and smoke emissions but slightly increase fuel consumption. The study concluded that biodiesel-diesel-ethanol blend can be used as a substitute of petro-diesel fuel to reduce dependency on fossil fuel as well as the exhaust emissions of the engine.[10]

To overcome the drawback of using diesel, a new fuel concept called WDF was proposed in recent years. WDF refers to fuels with a wide distillation range from initial boiling point (IBP) of gasoline to final boiling point (FBP) of diesel. As a short-term solution, WDF by blending gasoline and diesel has been studied for years.[11]

Petroleum reserves are rapidly and continuously depleting at an alarming pace and there is an urgent need to find alternative energy resources to control both, the global warming and the air pollution, which is primarily attributed to combustion of fossil fuels. In last couple of decades, biodiesel has emerged as the most important alternative fuel candidate to mineral diesel. Numerous experimental investigations have confirmed that biodiesel results in improved engine performance, lower emissions, particularly lower particulate mass emissions and is therefore relatively more environment friendly fuel, being renewable in nature. This review paper presents the effect of biodiesel and its blends on exhaust particulate’s physical characteristics (such as particulate mass, particle number-size distribution, particle surface area-size distribution, surface morphology) and chemical characteristics Control of particulate emissions using various engine control parameters such as intake air boosting using turbocharging, high pressure fuel injections, multiple injections, exhaust gas recirculation (EGR), and after-treatment devices are included in this review article.[12]

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NOx) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fuelled engines because of the convergence of one or more of three factors. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fuelled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.[13]

The oxygen enriched combustion of diesel engines can reduce smoke emission and increase engine thermal efficiency; however it can also lead to an increase of NO_x emission. In this paper, experiment was conducted on a turbocharged direct injection diesel engine, and oxygen-enriched and EGR techniques were used to produce lower NO_x–Smoke emission than the unmodified engine under the same fuel supply rate curve and fuel supply quantity. The specific fuel consumption and the power loss were lower than 5% compared to the unmodified engine. The results revealed that the optimal NO–Smoke emission can be achieved at these conditions: 1600 rpm of engine speed, full load, 30–40% EGR rate and 21.5–22.5% of intake oxygen density; 2200 rpm of engine speed, full load, 20–45% EGR rate and 22–24% of intake oxygen density. [14]

Knocking combustion research is crucially important because it determines engine durability, fuel consumption, and power density ,as well as noise and emission performance. Current spark ignition(SI) engines suffer from both conventional knock and super-knock. The mechanism of super-knock has been recently revealed in rapid compression machines (RCM) under engine-like conditions. Finally, suppression methods for conventional knock and super knock in SI engines are reviewed, including use of exhaust gas recirculation(EGR). This paper provides deep in sights into the processes occurring during knocking combustion in spark ignition engines. [15]

Diesel fuelled engines emit higher levels of carbon dioxide and other harmful air pollutants (such as noxious gases and particulates) per litre of fuel than gasoline engines. Improving the compression ignition engine is a direct way of going green. Reducing the harmful emissions can be achieved by future developments in the engine technology but also the implementation of alternative fuels. Hydrogen is a renewable, high-efficient and clean fuel that can potentially save the future of diesel-type engines. The evolution of high efficiency renewable hydrogen production methods is the most important path for the start of a new hydrogen era for the compression ignition engine that can improve its sustainability and maximum efficiency. This paper provides a detailed overview of hydrogen as a fuel for compression ignition engines.[16]

Environmental concerns and limited amount of petroleum fuels have caused interests in the development of alternative fuels for internal combustion (IC) engines. As an alternative, biodegradable, and renewable fuel, ethanol is receiving increasing attention. Therefore, in this study, influence of injection timing on the exhaust emission of a single cylinder, four stroke, direct injection, naturally aspirated diesel engine has been experimentally investigated using ethanol blended diesel fuel from 0% to 15% with an increment of 5%. The experimental test results showed that NOx and CO₂ emissions increased as CO and HC emissions decreased with increasing amount of ethanol in the fuel mixture. When compared to the results of original injection timing, NOx and CO₂ emissions increased, and unburned HC and CO emissions decreased for all test conditions. [17]

Exhaust Gas Recirculation (EGR) is a potential option for controlling in-cylinder NOx in automobiles. This paper aims to study the effect of EGR on NOx emissions and in Compression Ignition (CI) engines at various conditions. External EGR is then implemented to study its effect on engine-out emissions under cold start conditions.[18]

Vehicles are the main sources for environmental pollution especially those associated with diesel engines. It causes a number of health diseases and harm to the ecosystem. It is very urgent to find alternative fuel for vehicles. Biofuel is an alternative for vehicles which have potential to reduce engine emissions and maintain the air quality better. In recent years, worldwide biofuel production and use raised drastically. Some developed countries have put their target and mandate to use biofuel. The aim of this review is to discuss the impact of biofuel on diesel engines emission. From this review it is found that biofuel significantly reduces engine emissions and it has potential to reduce more than 80% of GHG emission. Finally, biofuel can be a viable alternative to be used as a transportation fuel.[19]

Dilution of the intake air of the SI engine with the inert gases is one of the emission control techniques like exhaust gas recirculation, water injection into combustion chamber and cyclic variability, without scarifying power output and/or thermal efficiency (TE). This paper investigates the effects of using argon (Ar) gas to mitigate the spark ignition engine intake air to enhance the performance and reduce the emissions mainly nitrogen oxides. The input variables of this study include the compression ratio, stroke length, and engine speed and argon concentration. Output parameters like Thermal Efficiency, volumetric efficiency, heat release rates, brake power, exhaust gas temperature and emissions of NOx, CO₂ and CO were studied, under variable argon concentrations. Results of this study showed that the inclusion of Argon to the input air has significantly improved the emission characteristics and engine’s performance within the range studied.[20]

References[edit]

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