Internal Combustion Engine Fundamentals †Free Sample to Students

Question: Discuss about the Internal Combustion Engine Fundamentals. Answer: Introduction: Dimethyl Ether (DME) is an organic isomer of ethanol, it is chemically represented as CH3OCH3 (Semelsberger, Borup and Greene 2006). It is a colorless, volatile, non-poisonous, liquid compound used as fuel, aerosol, propellant, solvent and refrigerant (Semelsberger, Borup and Greene 2006). When DME burns a blue flame is observed (Semelsberger, Borup and Greene 2006). Both liquid petroleum gas (LPG) and diesel could be replaced by dimethyl ether. A variety of raw materials like natural gas, crude oil, residual oil, coal and waste products have been used to produce DME (Azizi, Rezaeimanesh, Tohidian and Rahimpour 2014). Among these raw materials natural gas management is the prominently used as it is widely available (Azizi, Rezaeimanesh, Tohidian and Rahimpour 2014). DME is synthesized either using the direct route by directly synthesizing DME from syngas using a single stage bi-functional catalyst or the indirect route by producing methanol from syngas and then purifying it and converting it to DME (Azizi, Rezaeimanesh, Tohidian and Rahimpour 2014). The advantages and disadvantages of using DME are that it has a high cetane number (Huang, Wang, Chen, Zhou and Jiang 1999), due to which it has better combustion quality than diesel management. Therefore, an engine designed to run on DME would have better efficiency and mileage. DME has no carbon-to-carbon bonds (Huang, Wang, Chen, Zhou and Jiang 1999) as shown in Fig.1 so it reduces particulate emissions (Sorenson and Mikkelsen 1995) and eliminates the need for costly diesel particulate filters. DME requires a fuel tank twice in size as that needed for diesel because it has half the energy density of diesel (Semelsberger, Borup and Greene 2006). DME has lower viscosity than diesel which increases leakage in pumps and fuel injectors (Semelsberger, Borup and Greene 2006). The lubrication issues present while using DME causes premature wear and failure of pumps and fuel injectors (Semelsberger, Borup and Greene 2006). In a diesel engine fuel mixed with air ignites under high pressure and temperature (Taylor 1966). This type of combustion is heterogeneous and takes place at constant pressure (Taylor 1966). Unlike spark ignition engines, compression ignition engines have no tendency to knock, hence they can operate at significantly higher compression ratios and have better efficiency (Heywood, 1988). In diesel engine fuel is injected at the end of the combustion stroke and burns mostly as a diffusion combustion which enables lean burn, thereby improving the thermal efficiency (Taylor 1966). A three-way catalyst cannot be used for after treatment due to the lean burn mode which complicates the after treatment system, thus increasing the cost and emissions (Heywood, 1988). GT-suite is a popular simulation software developed by Gamma Technologies which is predominantly used for 1D simulation studies. It is used to study gas exchange rate and combustion simulations using a 1D unsteady, non-linear Navier-Stokes equation. It finds application in understanding the effects of combustion, heat transfer, evaporation, turbulence and so on. There are two kinds of combustion models in GT-Power. Non predictive combustion model:- In this model the burn rate is imposed and does not depend on the in cylinder conditions to characterize combustion and emission patterns (Gamma Technologies, 2015). It has fast simulation time and is used to evaluate the concepts that do not have an impact on the burn rate characteristics, but is not used to study the concepts that have an impact on burn rate like injection timings (Gamma Technologies, 2015). Predictive combustion model:- In this model the burn rate is calculated for each cycle based on the in cylinder conditions. It is used to study the concepts that have an impact on the burn rate but requires longer simulation time (Gamma Technologies, 2015). Phenomenological predictive combustion models make use of zone modelling, where the combustion is modelled to take place in single or multiple zones. In single zone combustion model injection, evaporation, mixing and subsequent burning of fuel happen in a single zone (Barba, Burkhardt, Boulouchos and Bargende 2000). Whereas multi zone models work by dividing injected fuel packets into multiple zones, each of these zones are treated as open systems (Jung and Assanis 2001). Multi zone combustion provides better spatial resolution compared to single zone models thereby enabling better prediction of performance and emission related parameters (Jung and Assanis 2001). GT-suite software used to model diesel engine is discussed in the su cceeding section. GT-Suite software has two specific multi zone combustion models for diesel engines namely DI-Jet and DI-Pulse (Gamma Technologies, 2015). DI-Jet Combustion model:- It is a multi-zone, multi-phase, quasi-dimensional model wherein the injected fuel is divided into a number of axial splices, each containing five radial zones (Gamma Technologies, 2015).. Each zone is further subdivided into subzones containing liquid fuel, vapour-air mixture and burned gas (Gamma Technologies, 2015). This type of multi zone approach yields better prediction about emissions of the engine. DI-Pulse Combustion model:- It is a phenomenological, multi-zone combustion model used for predicting in-cylinder combustion and emission parameters for direct injection diesel engine (Gamma Technologies, 2015). It is a three zone combustion model which is significantly quicker than DI-Jet model (Gamma Technologies, 2015). This is achieved by dividing the cylinder volume into three discrete thermodynamic zones, namely the main unburnt zone, the spray unburnt zone and the spray burnt zone each with its own temperature and concentration (Gamma Technologies, 2015). Therefore, GT-Suite is a powerful software for conducting simulation studies in diesel engines. It has the requisite tools to evaluate the performance and emission characteristics of any diesel engine. Literature indicates that DME improves the emission characteristics of diesel engine without compromising on performance. GT-Suite could be used as an effective tool to validate the same. Research has to be carried out in reducing the size of the fuel tank, elimination of leakage in pumps and fuel injectors and improving DMEs lubrication properties so as to reduce the wear and tear of pumps and fuel injectors. References Semelsberger, T.A., Borup, R.L. and Greene, H.L. (2006). Dimethyl ether (DME) as an alternative fuel. Journal of Power Sources, 156, pp. 497-511. Azizi, Z., Rezaeimanesh, M., Tohidian, T. and Rahimpour, M.R. (2014) Dimethyl Ether: A Review of Technologies and Production Challenges management. Chemical Engineering and Processing, 82, pp. 150-172. Huang, Z.H., Wang, H.W., Chen, H.Y., Zhou, L.B. and Jiang, D.M. (1999). Study on combustion characteristics of a compression ignition engine fuelled with dimethyl ether. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 213(D), pp. 647-652. Sorenson, S.C. and Mikkelsen, S.E. (1995). Performance and Emissions of a 0.273 Liter Direct Injection Diesel Engine Fueled with Neat Dimethyl Ether. SAE Technical Paper, 104(4), pp. 80-90. Taylor, C.F. (1966). The Internal-Combustion Engine in Theory and Practice. Cambridge: The MIT Press. Heywood, J.B. (1988). Internal combustion engine fundamentals. New York: McGraw-Hill. Gamma Technologies. (2015). GT-SUITE: Engine Performance Application Manual version 7.5. Westmont: Gamma Technologies. Barba, C., Burkhardt, C., Boulouchos, K. and Bargende, M. (2000). A Phenomenological Combustion Model for Heat Release Rate Prediction in High-Speed DI Diesel Engines with Common Rail Injection. SAE Technical Paper. Jung, D. and Assanis, D. (2001). Multi-Zone DI Diesel Spray Combustion Model for Cycle Simulation Studies of Engine Performance and Emissions. SAE Technical Paper. 110(3).