IJFEAT INTERNATIONALJOURNALFORENGINEERINGAPPLICATIONSAND TECHNOLOGY TITLE: EXHAUST GAS HEAT RECOVERY SYSTEM FOR I.C. ENGINE P.R. Ubarhande 1, Saurabh Jagdish Sankhe 2 1 Asst. Prof, Mechanical Department, Anuradha Engineering College, Maharashtra, India, prashant7.u@gmail.com 2 Student, Mechanical Department, Anuradha Engineering College, Maharashtra, India, saurabhjsankhe@gmail.com Abstract The focus of the study is to review the latest development and technologies on waste heat recovery of exhaust gas from internal combustion engine. These includes Rankine Cycle, Thermoelectric Generator (TEG), Active coolant warm up system, Exhaust gas oil heat exchanger and Cylinder head bypass with exhaust gas oil heat exchanger. Furthermore the study looked into the potential energy saving and performances of those technologies. The current world wide trend of increasing the energy demand, many segments that is responsible for growing share of fossil fuel usage and indirectly contributes in co 2 emission. It is hope with latest research on exhaust heat recovery system to increase the efficiency of I.C. engine, world energy demand on the depleting fossil fuel reserves would be reduced and hence the impact of global warming due to the co 2 emission would be reduced. Index Terms: Waste Heat in I.C Engine, Exhaust Gas Recovery System for I.C Engine, Engine, Waste Heat Recovery ------------------------------------------------------------***--------------------------------------------------------------- 1. INTRODUCTION1 The internal combustion engines are the major consumer of fossil fuel in the whole world. From the total heat supplied to the engine in the form of fuel, approximately, 30 to 40% is converted into useful mechanical work. The heat which remains is expelled through exhaust gases to the environment and engine cooling systems, resulting serious environmental pollution and also entropy rises, so it is required to utilized waste heat into useful work. The recovery and utilization of waste heat conserves fuel, usually fossil fuel and reduces the amount of waste heat. Given the importance of increasing energy conversion efficiency for reducing both the fuel consumption and emissions of engine, scientists and engineers have done lots of successful research aimed to improve engine thermal efficiency with supercharge, mixture of lean for combustion, and many more. From all the energy saving technologies studied. Exhaust Gas Heat Recovery System for I.C engine is considered to be one of the most effective. Researchers have recognize that Exhaust Gas Heat Recovery System from engine has the potential to decrease fuel consumption without increasing emissions, and recent technological advancements have made these systems viable and cost effective[6]. This paper gives a comprehensive review of the waste heat from internal combustion engine, waste heat recovery system and methods of waste heat recovery. 2. WASTE HEAT FROM I.C ENGINE2 Waste heat is heat, which is generated in a process by way of fuel combustion or chemical reaction, and
then dumped into the environment even though it could still be reused for some useful and economic purpose. This heat depends in part on the temperature of the waste heat gases and mass flow rate of exhaust gas. Waste heat losses arise both from equipment inefficiencies and from thermodynamic limitations on equipment and processes. For example, consider internal combustion engine approximately 30 to 40% is converted into useful mechanical work. The remaining heat is expelled to the environment through exhaust gases and engine cooling systems. It means approximately 60 to 70% energy losses as a waste heat through exhaust (30% as engine cooling system and 30 to 40% as environment through exhaust gas). Exhaust gases immediately leaving the engine can have temperatures as high as 842-1112 F [450-600 C]. Table 1: Various Engines with Their Output [5] Sr. No. Engine Type Power Output (kw) Waste Heat 1 Small air cooled diesel engine 35 2 Small agriculture tractor and construction 150 machine 3 Water air cooled engine 35-150 4 Earth moving machineries 520-720 5 Marine application 150-220 6 Truck and road engine 220 30-40% of Energy waste loss from I.C. Engine 3. CALCULATION FOR WASTE HEAT FROM I.C ENGINE3 3.1 AVAILABLE WASTE HEAT1 The quantity of waste heat contained in exhaust gas is a function of both the temperature and the mass flow rate of the exhaust gas: Q = m C p T Where,(Q) is the heat loss (kj/min);(m) is the exhaust gas mass flow rate (kg/min);(c p ) is the specific heat of exhaust gas (kj/kg K); and ( T) is temperature gradient in K. In order to enable heat transfer and recovery, it is necessary that the waste heat source temperature is higher than the heat sink temperature. Moreover, the magnitude of the temperature difference between the heat source and sink is an important determinant of waste heat s utility or quality. The source and sink temperature difference influences the rate at which heat is transferred per unit surface area of recovery system, and the maximum theoretical efficiency of converting thermal from the heat source to another form of energy (i.e., mechanical or electrical). Finally, the temperature range has important function for the selection of waste heat recovery system designs. Table2: Temperature range from Diesel Engine Sr. Engine Temperature in C No. 1 Single Cylinder Four Stroke Diesel Engine. 456 2 Four Cylinder Four 448 Stroke Diesel Engine. 3 Six Cylinder Four 336 Stroke Diesel Engine. (Ref- this temperature was taken from survey done on various internal combustion engines.)[3] 3.2 HEAT LOSS THROUGH EXHAUST2 Engine and dynamometer specification is given in table (3) and (4). Heat loss through the exhaust gas from internal combustion is calculated as follows. Assuming, Volumetric efficiency ( v ) is 0.8 to 0.9 Density diesel fuel is 0.84 to 0.85 gm/cc Calorific value of diesel is 42 to 45 MJ/kg Density air fuel ( a ) is 1.167 kg/m3 Specific heat of exhaust gas (c p ) is 1.1-1.25 KJ/kg K Table 3: Specification of Engine. Engine Single cylinder, 4- Stroke. Vertical stationary C.I. Engine. Bore 87.5mm Stroke 110mm Comp ratio 17.5 Capacity (v s ) 661cc (0.66 Ltrs) Power 8hp (5.9kw) at 1800 rpm Sp.Fuel Combustion 220 gms /kw-hr (0.22 kg/kwhr) RPM 1800 BHP @ 1800 rpm 5.9kw Cooling System Water cooled. Table 4: specification of Dynamometer Type Rope Brake Type Dynamometer Diameter of Rope 25mm Diameter of Brake 255 mm Drum Effective Radius R= (225=25)/2 =140mm
Exhaust heat loss through diesel engine; Compression ratio (v r ): V r = 17.5 +6.61 10-4 Clearance volume ( ) = 4 10-5 m 3 Total Volume ( ) = = 4 10 5 + 6.61 10-4 = 7.01 10-4 m 3 Mass flow rate of fuel (on the basis of specific fuel consumption). s.f.c. = = s.f.c power = 220 5.9 = 0.3177 ec volume rate = swept volume speed volume rate (v) = N v = 6.61 10-4 v =0.4957 v =8.262 10-3 Volumetric efficiency ( ) ( ) = = = n = 0.9 1.16 6.61 10-4 = 0.5175 = 8.62 Mass flow rate of exhaust gas = = 8.625 + 0.3177 = 8.9427 = 8.9427 10-4 Heat loss in exhaust gas (Q) Q= T 8.9427 10-3 1.1 (450-30) 4.13 KJ/Sec (KW). 4. UTILIZATION AND ADVANCE WASTE HEAT RECOVERY SYSTEMS4 4.1. Utilization1 The input energy is divided into roughly three equal parts: energy converted to useful work, energy transferred to coolant and energy lost with the exhaust gases. There are several technologies for recovering this energy on an internal combustion engine, where as the dominating ones are: Waste heat can utilized for heating purpose, power generation purpose, etc. 4.1.1 Heating purpose1 Waste heat recovery system can utilized for pre heating intake air and intake fuel. Result shows that NOx emission is reduced with the new air preheating waste heat recovery setup. Higher inlet air temperature is caused the lower ignition delay, which is responsible for lower NOx formation with air preheating. Uniform or better combustion is occurred due to pre heating of inlet air, which also causes lower noise of engine. They have represented easy vaporization and better mixing of air and fuel occur due to warm up of inlet air, which causes lower CO emission. Heat energy is recovered from the exhaust gases, which causes lower heat addition, thus improving engine thermal efficiency. 4.1.2 Power generation2 Waste heat can also be utilized indirectly for the power generation using Rankine cycle. Bryton cycle, Stirling cycle and directly used for thermoelectric generator etc, Generating power from waste heat typically involves waste heat utilization from internal combustion engine to generate mechanical energy that drives an electric generator. Electricity generation is directly from heat source such as thermoelectric and piezoelectric generator. A factor that affects on power generation is thermodynamic limitations for different temperature range. The efficiency of power generation is heavily depended on the temperature of the waste heat gas and mass flow rate of exhaust gas. 4.2 Advance waste heat recovery systems2 4.2.1 Rankine Cycle1 The system is based on the steam generation in a secondary circuit using the exhaust gas thermal energy to produce additional power by means of a steam expander. A special case of low temperature energy generation systems uses certain organic fluids instead of water in so -called Organic Rankine Cycle (ORC). Waste heat recovery from
Rankine cycle operated at low temperature difference using unconventional fluids (refrigerants, CO2, binary mixtures) is shown in fig 1. At very low heat source temperature the transcritical CO2 cycle produces highest net power output. Rankine bottoming cycle techniques maximize energy efficiency; reduce fuel consumption and green house gas emissions. Recovering engine waste heat can be achieved via number of methods. The heat can either be reused within the same process or transferred to another thermal, electrical, or mechanical process. Investigation and market evaluation of Organic Rankine cycle can be applied in several cost effectively areas. Analysis shows that evaporator pressure gives better efficiencies. Pinch point temperatures, heat exchangers cost, critical temperature of working fluid would be a restriction for maximum working pressure of cycle. Organic Rankine cycles as in Combined Heat and Power units are options to improve total efficiency and reduce the cost. Thermoelectric method of exhaust gas waste heat recovery of a three cylinder spark ignition engine is carried on experimental based test. Waste heat recovery using Organic Rankine cycle is an efficient method compared with the other techniques; so auto mobile manufacturers use this method to enhance the efficiency of their products. The heat recovery is can be done and increases with increasing exhaust mass flow rate. The most important question regarding safety relates to working fluid. Water alone gives a higher efficiency and allow smaller heat exchanger system sizes but unfortunately water can t be used as a working fluid if the vehicle is operated below 0 C. ethanol has a very low critical flash point of only 16.6 C and there for need explosive protection. If the evaporator would leak and ethanol would run onto the heat exhaust which would immediately cause a fire. The effects on the vehicles performance are expected to be very small, similar to the fuel economy. The alternator has to work less hard but the additional weight would partially compensate that. Regarding noise the steam turbine would lead to noise problem similar to those known from turbo charger, but they can be managed in a similar way. The packaging of the additional component: the condenser needs to be located in the front of the normal radiator to that the radiator size need to be increased. 4.2.2 Thermo-electric Generator2 Thermoelectric generators are all solid-state devices that convert heat into electricity. Unlike traditional dynamic heat engines, thermoelectric generators contain no moving parts and are completely silent. Compared to large, traditional heat engines, thermoelectric generators have lower efficiency. But for small applications, thermoelectrics can become competitive because they are compact, simple. Thermoelectric systems can be easily designed to operate with small heat sources and small temperature differences. Such small generators could be mass produced for use in automotive waste heat recovery or home cogeneration of heat and electricity. Fig 1: Rankine Cycle The economic feasibility of waste heat recovery from diesel engine exhaust gas and analysis of harmfulness of the gases was done by using the methods of purification and processing diesel engine exhaust gas. The computational model developed which determine diesel exhaust emission rate and diesel exhaust waste heat rate and found useful results for diesel engine. Fig 2: Thermo-electric Generator
A thermoelectric produces electrical power from heat flow across a temperature gradient. As the heat flows from hot to cold, free charge carriers (electrons or holes) in the material are also driven to the cold end fig 2. The resulting voltage (V) is proportional to the temperature difference ( T) via the Seebeck coefficient α, (V = α T). By connecting an electron conducting (n-type) and hole conducting (p-type) material in series, a net voltage is produced, that can be driven through a load. A good thermoelectric material has a Seebeck coefficient between 100 µv/k and 300 µv/k; thus, in order to achieve a few volts at the load, many thermoelectric couples need to be connected in series to make the thermoelectric device. The cost of such TEG system is expected to be similar to the Rankine cycle system because similar numbers of components are required. Safety impact will be largely influenced by the type of material that will be used. Many of the material studied are heavy metals that are quite safety critical, lead, tellurium and bismuth are toxic, so special pre caution are required. The performance impacts are expected to the similar to the compared to a Rankine System due to its low weight. No changes to the regulated emission are expected or have been repeated. No rotating parts are required which will minimize the maintenance requirement. A volume of between 1.71 and 3.61 should be relatively easy to package. 4.2.3 Active coolant warm up system3 It is the system which warms the coolant faster and should also warm up the oil faster so that friction can be reduced. The benefit of this approach has been tested in various passive warm up technologies for eg: split cooling system where the cooling system is separated into a lower temperature circuit for the cylinder head and a high temperature circuit for a cylinder block. Electric water pump that provide coolant and demand or electric thermostat that change the thermostat opening temperature to achieve higher cylinder linear temperature under the moderate load. Systems with exhaust gas heat exchanger that warm up the coolant appear to be very attractive due to their simplicity. These active coolants warm up have a heat exchanger installed after the catalyst as shown in fig 3. A three way exhaust flap valve control the exhaust flow between an exhaust bypass and heat exchanger: during low coolant temperature exhaust gas warm up the coolant. Once the coolant reaches the threshold temperature the flap redirect the exhaust gas away from the heat exchanger through a bypass. On the coolant side the heat exchanger can be installed in different location for eg: between the engine and the cabin heater. Exhaust Fig 3: Active coolant warm up system The cost is expected to be moderate with only one or two additional heat exchanger and some values that can be integrated. The system is also easier to package although, it could be different to find the right space for vehicle with high performance engine. For safety, reliability, performance, regulated emission is expected to be similar to the base line configuration. For maintenance the some might be apply the special design. Considerations are required to deal with the larger amount of condensed water that can freeze below 0 C. 4.2.4 Exhaust Gas/ Oil Heat Exchanger4 As we have studied the principle of active coolant warm up system the principle of exhaust gasoil heat exchanger is same. The only difference is that the exhaust gas heat is directly transferred to the engine oil instead into the coolant. The same heat exchanger is used and connected to the engine oil system between the engine block and the oil filter by using a sandwich oil cooler adapter. The benefits of warming up the oil directly are the heat loss to the ambient is reduced so that most of the exhaust heat can be transferred directly into the engine oil where the friction is reduced. The specific heat capacity of the oil is smaller compared to the coolant so the thermal inertia is reduced. The higher oil temperature resulted in lower oil pressure and therefore lower pressure is required for oil pump. For cost and packaging the same applies as for coolant exhaust gas heat exchanger. In a case where the heat exchanger could leak oil could run onto the
heat exhaust were it could catch fire, because it is installed in pressure side of the lubrication system. The heat exchanger needs higher safety margin. The engine performance is expected to improve during the warm up phase due to higher oil temperature. The maintenance requirements of on engine run at higher oil temperature even during in city driving. That reduced wear and the oil change interval can be extended Fig 4: Exhaust Gas/ Oil Heat Exchanger 4.2.5 Cylinder head bypass with exhaust gas oil heat exchanger5 A future variation of exhaust gas heat exchanger is described in [2]. Here the exhaust gas heat exchanger is installed in an oil bypass between the cylinder head oil gallery and the oil pump. With this arrangement the heat is move from the higher pressure side of the lubrication system up to the suction side. That make such arrangement much safer as the chances for oil to leak from the heat exchanger on to the exhaust system are significantly reduced. The flow through the bypass is controlled by valve to ensure optimum and reliable oil pressure under all operating condition, which eliminate another key weakness of the previous system. Due to the lower pressure on the liquid (oil) side compared, to the previous system and even compared with the coolant exhaust gas heat exchanger the required safety factors are potential worst case condition can be reduced. There are also numbers of benefits related to fuel economy. The bypass from the cylinder head to the oil pump already reduces the oil pressure during the cold start similarly as variable oil pump so there is no need for the oil pump pressure relive valve to open. The thermal inertia of the oil in the engine oil galleries are partially separated from the oil sump. That means the oil pan warm up slower, but the combined air flow warms up faster. The heat loss from the oil pan is reduced due to lower oil sump temperature. The oil flow rate through the cylinder head oil galleries is increased and consequently heat transferred from combustion gas to the oil increases, leading to the
faster warm up. The diameter of oil bypass hoes can be much smaller compared to heat exchanger between oil filter and engine block. This reduces the thermal inertia of the oil in by pass and heat exchanger. The costs are expected to be slightly higher compared to the previous system. Emission, NVH (Noise Vibration Harness), package, maintenance and weight are also expected to be similar. Performance and cabin warm up are expected to be slightly better due to the same effects that help to improve fuel efficiencies. Fig 5: Cylinder head bypass with exhaust gas oil heat exchanger [4]
CONCLUSION In an attempt to explore the possibilities of waste heat recovery in an IC engine, there are large potentials of energy savings through the use of waste heat recovery technologies. Waste heat recovery defines capturing and reusing the waste heat from internal combustion engine for heating, generating mechanical or electrical work and refrigeration system. Five different advance waste heat recovery system have been compared to a set of 12 important valuation criteria as displayed in table. An oil bypass from the cylinder head to the pump with an integrated exhaust gas heat exchanger and oil flow control valve has the potential for the largest % fuel economy improvement. Further benefit are significant emission reduction, moderate cost, and longer oil change interval. The second best option is an oil exhaust gas heat exchanger between oil filter and engine block without the cylinder head bypass. The important for fuel economy and other attribute are also significant. The coolant exhaust gas heat exchanger can only provide marginal fuel economy benefit during the NEDC (New European Drive Cycle) test. The biggest advantage is to improve cabin warm up performance. Thermo-Electric and Rankine cycle system only deliver minor fuel economy benefit over the NEDC test. Table 5: Comparison and calculation of all five advance waste heat recovery system [4].
ACKNOWLEDGEMENT This paper shows the different methods of using exhaust gas heat of I.C engine. All the methods are compared on twelve parameter.special thanks to all those who have helped me for making it successful. REFERENCES [1] Schwarze. H., Brouwer, L., Knall,G., Schlerege, F., Miiller- Frank, U.Kopnarski. M., Emrich, S., Olalterung and Verschlei. Im Ottomator: MTZ, 2008-10 (Germany) [2] Will.F., Process And Device For Lubrication Of Rotating And Oscillating Components, Patent application no.de 102009013943.5 field 19/03/2009 (Germany) [3] Will.F. A Novel Exhausts Heat Recovery System To Reduce Fuel Consumption F2012A073, FISTIA conference Budapest Hungry 2010. [4] Will.F. Comparison of Advance Waste Heat Recovery System With A Novel Oil Heating System. International Journal Of Automation Engineering 4 (2013) 33-40 30134100, (Australia) [5] J.S Jadhao, DG. Thombare, Review on Exhaust Gas Heat Recovery for I.C. Engine, International Journal of Engineering and Innovation Technology (IJEIT) Volume 2, issue 12, June 2013. [6] Hakan Özcan, M.S. Söylemez, Thermal Balance Of A LPG Fuelled, Four Stroke SI Engine With Water Addition, Energy Conversion and Management 47 (5) (2006) 570-581. [7] P. Sathiamurthi, Design And Development Of Waste Heat Recovery System For Air Conditioning, Unit European Journal of Scientific Research, Vol.54 No.1 (2011), pp.102-110, 2011.