Direct Exhaust heat recovery into Water cooled Charge Air Cooler as technical brick for improved cold start functionality

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1 Direct Exhaust heat recovery into Water cooled Charge Air Cooler as technical brick for improved cold start functionality Zoulikha Soukeur 1, José Borges-Alejo 1, José Manuel Luján 2, Héctor Climent 2, Ausias Moratal 2 1: Valeo Thermal Systems, R&D Advanced Development, La Verriere, France 2: CMT Motores Térmicos, Universitat Politècnica de València, Spain Abstract: Further reduction of pollutant emissions and fuel consumption is one of the major challenges that automotive engineers currently have to overcome. Low ambient temperature testing for diesel engines will be mandatory in the near future, making cold engine start and warm up analysis important topics for researchers. In order to improve the engine operation under those critical conditions, different systems have been proposed in recent years. Previous studies have shown that heating the intake air is one of the most effective solutions to boost engine performance during warm up. In this paper a novel exhaust heat recovery system combined with a Water cooled Charge Air Cooler is presented. A gas/liquid heat exchanger, the Twin Function Exchanger, fulfilling two different functions is firstly used to recover energy from the exhaust side transferring it to the intake, and later as low pressure EGR cooler. Moreover, a complete thermal management strategy to control the intake air temperature has been put in place in order to optimize the engine behavior to be as close as possible as running conditions at 20 C. Experiments were carried out in transient load conditions of NEDC and WLTC cycles with a 2.0 liter turbocharged diesel engine, installed in a climatic test cell. Using this new system, intake air temperature was increased improving the combustion process during the engine warm up at -7 C. Important benefits on HC and CO were obtained in both cycles 1. Introduction Increasingly stringent emissions regulations are constantly motivating the automotive industry to develop new systems and strategies. As automotive cycles are being more restrictive, it is expected that the operation conditions of the test drive will consider the effect of running at lower ambient temperature. Under these conditions, fuel consumption and pollutant emissions during the engine warm-up are critical. According to the literature [1] and [2], unburned hydrocarbons and carbon monoxides are mainly emitted when engine temperatures remain low. Therefore, a non-negligible effect of the low engine temperature on pollutant emissions during engine warm up is noticed [3]. In this sense, it is proved that under certain conditions, intake air heating can provide benefits such as HC and CO emissions reduction [4], combustion noise control and engine stability improvement after cold starting [5]. Researchers have studied the effect on pollutant emissions and engine performance in cold driving cycles [6]. Currently, the U.S Environmental Protection Agency includes a cold cycle of FTP-75 as an optional driving cycle carried out at -7 ºC. It is expected that if future regulations include cold cycles as mandatory, they will be assessed at this temperature. Many authors have researched different ways to get improvements on engine thermal conditions for cold operation. Gumus et al. [7] present a thermal energy storage device (TESD) connected to the engine water jacket, that works on the effect of absorption and rejection of heat during the solid liquid phase change of heat storage material (Na 2 SO 4-10H 2 O). Preheating engine at cold start, at 2 ºC, Gumus obtained a CO and HC emission decrease about 64% and 15% respectively. Broatch et al. [8] evaluated the potential of an intake air heating technology, by means of electrical heaters, for the reduction of pollutant emissions from diesel engine combustion during an NEDC cycle. Results showed a reduction of 13% in HC, 5% in CO and 3% in NOx but particulate matter increases about 4%. Kauranen [9] proposes a double heat recovery system from the combination of exhaust gas heat recovery system and latent heat accumulator for thermal energy storage, using the energy to heat the engine coolant during a cold start and low engine load. In this work a different concept is proposed. Exhaust thermal energy is recovered by a heat exchanger placed on the tail of the exhaust line. A specific coolant loop brings the recovered heat from the exhaust to a water / air heat exchanger that heats the intake air when requested. The capability of the exhaust heat recovery system was investigated as well as the influence of the intake air temperature on emissions and performance of a DI Diesel engine working under transient load conditions at low ambient temperatures. The aim of this research is to analyze how the improvement of combustion boundary conditions, such as air intake temperature, can enhance the engine performance under low temperature conditions. Summing up, the recovery system purpose is the warming-up time reduction, and the engine operation under better conditions, until engine nominal temperatures are reached. The paper is structured as follows. Section 2 is devoted to the experimental setup and the 1

2 explanation of the theoretical tools. Section 3 is focused on the heat exchangers effectiveness characterization. Section 4 contains the results and analysis of the recovery system: The intake air temperature management, the effects on the emissions and engine performance during the WLTC cycle starting at -7 ºC and the impact on the system of different ambient temperatures applied in NEDC cycles. Finally, the main conclusions and the perspectives are presented in sections 5 and Experimental setup and methodology 2.1. Description of test cell and setup In order to analyze the effect of the heat recovery system, experiments with an in line 4 cylinders, 2.0 l, turbocharged HSDI diesel engine were conducted. In Table 1 the features of the engine are shown. The original engine architecture did not dispose an LP EGR line, it was built ad hoc for this engine and installed in the test cell. The tests were carried out in a climatic chamber where the ambient, coolant and fuel temperatures are under control. cooling of the charge air according to the engine specifications. HP EGR duct is connected at one side of this short manifold and mixes the exhaust gas with the fresh air through a specific part called HP EGR rail, whose design has been optimized so as to avoid HP EGR dispersion between the cylinders [10]. The result is a compact Air Intake Module (AIM) in which lengths are reduced and therefore time response too. Figure 1 shows a drawing of the Air Intake Module. HP EGR DUCT WCAC Figure 1 : Air Intake Module The waste heat recovery system is based on a heat exchanger placed at the end of the exhaust line, in a Engine Intake manifold was a cutting edge design where the classic intercooler was replaced by a water/air heat exchanger, known as Water Charge Air Cooler (WCAC), which was integrated in a short intake manifold (AIM). The WCAC technology presents many benefits compared with a conventional Air Charge Air Cooler (ACAC). Its installation close to the engine permits among others to improve the engine response in transient conditions by reducing the volume of the charge air between the compressor and the engine. The AIM was completely made of aluminum. The exchanger core technology consists on plates and fins brazed together. It has been sized to ensure an efficient location that permits to recover all the energy available in the exhaust gas. The heat exchanger technology is based on Valeo EGR cooler technology and consists of stainless steel tubes and fins brazed. Figure 2 shows schematic layouts of the air path of the engine. The upper layout corresponds to the reference case and the bottom layout corresponds to the engine layout with the heat recovery system. As shown in the bottom layout, the heat exchanger in the exhaust line is used for, simultaneously LP EGR cooling and heat recovery. For this reason this unit will be referred as Twin Function Exchanger (TFE). The TFE is installed in the main exhaust line and is 2

3 able to recover energy since the start of the engine and even when no LP EGR is requested. In order to avoid any impact on the performance of the engine when full power is needed, an exhaust gas bypass branch has been added. As other heat recovery systems, one of the strengths of this system is that the energy recovered is a free energy that otherwise will be released to the ambient. The TFE improves the overall engine efficiency due to the use of the waste engine energy without extra cost. Intake air heating Hot exhaust gas HT coolant circuit TFE EHRS / EGRc WCAC Cooledexhaust gas Figure 3 : Coolant layout connected to the TFE. Above: EHRS mode. Below: EGR cooler mode Figure 2 : Above: Reference engine layout. Below: Heat recovery system engine layout Figure 3 shows schematics layouts of the coolant path around the TFE. In a first heat recovery mode called Intake air heating corresponding to the upper layout, the TFE is connected to the WCAC by means of a dedicated coolant circuit. The coolant is heated in the TFE using the exhaust gas enthalpy and releases heat to the intake air in the WCAC. In a second mode called EGR gas cooling, corresponding to the bottom layout, the TFE is connected to the high temperature coolant loop of the engine and works as a standard EGR cooler. No dedicated coolant loop is requested for this second mode. The heat recovery control moves along different modes depending on intake air and engine coolant temperatures. The coolant system enables different flow paths depending on the operation mode. Figure 4 depicts a more detailed schema of the coolant system that has been implemented and tested. In order to facilitate our experimental tests, instead of using a four way valve, two three way valves have been used. The valves V1 and V2 are regulated by the same signal. V1 guides the coolant flow leaving the TFE to either the high temperature coolant loop (to the engine) or to the low temperature coolant loop (to the WCAC). In this second case, an additional coolant valve V3 allows HT Radiator circulate the coolant either through the by-pass branch, either through the low temperature radiator or through both of them at the same time depending on the level of cooling requested. Standard HT coolant loop LT radiator by-pass Figure 4 : Coolant layout of the complete thermal management system 3

4 Table 2 presents the different operation modes of this new thermal management strategy. When the engine is running in cold conditions, the heat recovery system is enabled from the beginning of the test. Thermal energy is obtained from the exhaust and released to the intake by means of the WCAC. This no heat recovery system is installed in this case. On the other hand, the heat recovery test with the TFE installed at the end of the main exhaust line. For both kinds of tests, the same HP EGR and LP EGR combination was implemented. Due to the higher gas temperature and enthalpy, HP EGR is preferred for Table 2 Thermal management strategy. Mode Engine conditions Action Mode Heating mode Cold engine: WLTC/RDE cold start, winter driving conditions - TFE connected to WCAC - Exhaust heat recovery Heating mode Stand-by mode Warm-up in progress: Intake air temperature fine tuning, homogenization of temperature inside WCAC, avoid boiling risks - TFE connected to HT coolant loop - WCAC connected to by-pass Stand-by mode Regulation Regulation mode Warm-up in progress: Intake air temperature fine tuning - TFE connected to HT coolant loop - WCAC connected to by-pass and LT radiator Cooling mode Cooling mode Hot engine - TFE connected to HT coolant loop - WCAC connected to LT radiator heating mode is a new functionality given to this exchanger that not only cools down but also heats up the intake air. As the engine warm up proceeds, the external energy becomes less necessary. The standby mode stops the heat recovery but allows the flow to circulate inside the WCAC to homogenize the temperature inside. The exchanger is in a smart thermal management mode. Another mode of this new smart thermal management is applied once the temperature of the intake air increases a bit more. The system moves to a regulation mode where a certain percentage of coolant already cooled by the low temperature radiator is mixed with not cooled coolant. Once the engine reaches its nominal temperature, heat surplus has to be removed to avoid overheating, and the WCAC goes in a standard cooling mode. The heat recovery system was tested in NEDC and WLTC driving cycles. Several NEDC cycles were carried out in order to study the feasibility of the energy recovery system from low temperatures,-7 ºC, to higher and less critical temperatures, 0 C and 10 ºC. Regarding WLTC cycles, only tests at -7 C were performed. Two types of tests were carried out in both NEDC and WLTC cycles. On one hand, the reference test with no coolant flow strategy in the WCAC for the beginning of the test cycle, in order to reduce the negative effect of air cooling at low ambient temperatures. The WCAC coolant flow is turned on once the low load of the cycles is performed. In case of NEDC cycles the water pump is switched on at 800 seconds and in WLTC cycles at 450 seconds. In this paper the reference test is also named as 0-flow case. In the reference test the LP EGR cooler is installed in the standard LP EGR line, the first part of the cycles. At cold conditions, introducing LP EGR from the beginning could drive to misfiring events. Afterwards HP EGR is switched to LP EGR in order to take profit of its higher potential to reduce NOx emissions. Indeed, as LP EGR gas has lower temperature than HP EGR gas, the combustion peak temperature is reduced and therefore NOx emission too. In case of NEDC cycles HP EGR is switched to LP EGR at 180 seconds. In WLTC cycles, the switch between HP EGR and LP EGR is at the end of the low load cycle part, at 450 seconds. Horiba Mexa 7100 DEGR was used to measure O 2, CO 2, CO, using a non-dispersive infrared analyzer, and unburned hydrocarbons with a chemiluminescent detector. The error of the gas analyzer is in the range of 2%. Both intake and exhaust CO 2 measurements were recorded in order to obtain the EGR rates. The EGR rate is defined as: Where and are the mass flow of EGR gas and fresh air, respectively. Air mass flow was measured by a hot wire anemometer with a measurement error of 1%. Equation 1 can be expressed as a function of a specific pollutant concentration, like CO 2, measured in the intake and exhaust manifold [11]. Where, and are the carbon dioxide concentration in the intake, ambient and exhaust respectively. Fuel consumption along the driving cycle was measured with an AVL fuel balance, with a [1] [2] 4

5 measurement error of 0.2%. Temperatures at the intake were measured downstream and upstream the WCAC. Besides the main parameters, other variables were recorded, such as engine speed, fuel rate injection, boost pressure, air mass flow and exhaust temperatures with the aim to compare the repeatability of the cycles and obtain data to get a thermal characterization of both WCAC and TFE. All measurement signals were sampled at 10 Hz. Once the driving cycle has finished, the engine is put under specific conditions of load to regenerate the particulate filter [12]. After that, test cell is cooled for several hours in order to ensure the same initial conditions of all cycles carried out Repeatability and pollutant emissions calculation In addition to the errors of the measurement devices, engine performance and boundary conditions variability affects the result obtained. In order to quantify the variability pattern, the repeatability of the experiments was evaluated by comparing the exhaust emissions measurements and fuel consumption of several driving cycles carried out in different days at -7 ºC [13]. The repeatability study shows maximum variations of the total emissions about 4% for CO, 10% for HC and 2% in case of fuel consumption. For each variable: fuel, CO and HC, variability is characterized through the relative difference of each case compared to the average. The calculation of the error due to the variability, presented as, is shown in the Equation 3. Where represents the accumulated value of the variable under study, fuel, HC or CO, at each time.,, are the maximum, minimum and average amount respectively of the variable at each point of the driving cycle. Figure 5 shows the average of the accumulated values of fuel consumption and pollutant emissions along the NEDC cycle. The chart includes an error bar at the main points of the cycle. [3] The pollutant sample point is located upstream the Diesel oxidation catalyst to analyze the effect on pollutant emissions of the heat recovery system acting alone without taking into account the posttreatment system. Flow rate mass emissions are calculated using the pollutant concentrations and the air and fuel mass flow, according to the Equation 4, in order to know how much pollutants are released to the atmosphere. Where and are the molecular weight of pollutants and air respectively. [4] is the measured pollutant concentration and and are the mass flow of fresh air and fuel respectively. 3. Heat exchangers effectiveness characterization 3.1. Effectiveness of TFE and WCAC Heat exchanger effectiveness shows the temperature increase of a fluid respect the theoretical value that it could reach [14]. Effectiveness ( ) calculation of TFE are shown in Equations 5 and 6. Equation 5 shows the TFE effectiveness when it works as a heat recovery system. Where,, are the outlet coolant TFE temperature, inlet coolant TFE temperature and inlet gas temperature respectively. Equation 6 shows the cooling performance of the TFE when LP EGR is enabled. Where,,, are the inlet gas temperature, outlet gas temperature and inlet coolant TFE temperature respectively. Equation 7 shows the WCAC effectiveness when the heat recovery system is running. [5] [6] [7] Where,, are the outlet air temperature, inlet air temperature and inlet coolant WCAC temperature respectively. Large heat losses and thermal inertia of exchanger s core and housing reduce the effectiveness. It is important to remark that the thermal inertia works as an energy storage which at thermal transient conditions can demand or release heat. In addition, the heat capacities of fluids affect to the temperatures reached. Figure 5 : Accumulated pollutant emissions and fuel consumption at -7ºC in an NEDC cycle 5

6 3.2. TFE and WCAC performance Cycle-averaged TFE and WCAC effectiveness are calculated with Equations 5, 6 and 7. Equations 5 and 7 are applied while the heat recovery system delivers the energy from the exhaust to the intake air. Equation 6 is applied while LP EGR is enabled, in order to characterize the EGR cooling performance of the TFE. The effectiveness of the TFE and WCAC when the heat recovery system is working is 11% and 89% respectively. Both heat exchangers have been designed to work in counter flow configuration. TFE shows low effectiveness as a consequence of the large value of the coolant heat capacity compared to the exhaust gas. Coolant temperature increase is small and differences between the inlet gas and the outlet coolant temperatures are significant. On the other hand, WCAC effectiveness is high due to the reverse effect. The air heat capacity is low, so air temperature reaches the coolant inlet one. Regarding the LP EGR cooling performance of TFE the effectiveness is 94%. In this case the high effectiveness shows the important cooling effect of the TFE on the exhaust gas. 4. Engine performance results and discussion The heating recovery system was applied in NEDC and WLTC cycles at -7ºC of ambient temperature. Exhaust raw emissions were measured at the beginning of the exhaust line, between the turbine outlet and the inlet of the diesel oxidation catalyst. This section is organized as follows. Section 4.1 analyzes the effect of ambient temperature in engine performance in WLTC cycles without the heat recovery system installed. In section 4.2 the heat recovery system is analyzed for WLTC cycles performed at low ambient temperature conditions. Finally, section 4.3 is devoted to the heat recovery system performance depending on ambient temperature for NEDC cycles Assessment of engine performance at different ambient temperatures without heat recovery system in WLTC cycles. Figure 6 shows the relative difference of WLTC cycles performed at -7 ºC compared to those at 20 ºC in terms of pollutants emissions and fuel consumption. Significant hydrocarbons emissions increase is observed when cycles are performed at -7ºC. The hydrocarbon emission is the most temperature dependent pollutant. Carbon monoxide emission is more affected by transient load conditions than ambient temperature. At fast transient load conditions low air to fuel ratio is obtained and incomplete combustion occurs with the consequently releasing of partially oxidized chemical products like CO. The engine calibration was originally optimized for the NEDC cycle. As the WLTC cycle shows stronger transient load conditions than NEDC, a huge increase of CO emissions have been observed. In order to analyze the effect of ambient temperature on CO emissions independently of the effect of transient operation, the CO emissions have been recalculated removing the CO peaks recorded during the WLTC accelerations. These recalculated CO emissions called smoothed CO are shown in Figure 6. The increase of smoothed CO at -7 ºC is around 28%. Finally, slight higher fuel consumption is also recorded at -7 ºC, around 3%, as lower engine efficiency is obtained as temperature goes down. Figure 6 : Comparison of WLTC cycles at -7 ºC and 20 ºC: Pollutant emissions and fuel consumption 4.2. Assessment of heat recovery system performance at -7 º C in WLTC cycles In this section, temperatures, emissions and fuel consumption are compared between tests performed at -7º C ambient temperature. Figure 7 shows the WCAC inlet and outlet gas temperature of the heat recovery case. According to the chart, during the first 1000 seconds the WCAC outlet gas temperature is higher than the inlet due to the exhaust heat recovered. For the first 500 seconds the thermal system performs the strategy of heat recovery that according to the table 2 corresponds to the heating mode. During the heating mode the energy delivered by the WCAC to the intake air is 440 kj. The average power delivered is 0.83 kw and the maximum recorded is 1.83 kw. At 500 seconds the WCAC coolant temperature reaches 35ºC, so the thermal control actuates in order to keep a constant gas temperature. From this point of the cycle until the extra high load WCAC coolant temperatures varies between 35ºC and 43ºC that corresponds to the stand-by and regulation operation modes. Once extra high load loads are performed, at 1600 seconds, WCAC coolant temperature overcomes the limit of 43ºC and therefore the cooling mode is enabled. With this thermal control the WCAC outlet temperature is managed independently of the WCAC inlet temperature which is affected by the engine load. 6

7 Figure 7 : Heat recovery test at -7 C: WCAC inlet and outlet air temperatures Figure 8 compares the WCAC outlet gas temperature between the reference case and the heat recovery tests. As expected, a higher air temperature in the heat recovery test has been recorded. The thermal control implemented allows to keep the temperature quite stable once it has reached the target value of 35 ºC. The benefit of using the heat recovery system is noticeable, allowing to increase the intake gas temperature in a short time period. Figure 8 : WCAC outlet air comparison between tests at -7 ºC Figure 9 shows the intake air temperature evolution during the WLTC cycle at -7 C with the different configurations: 0-flow test as reference and the heat recovery system test. In the chart is also plotted the intake temperature of 0-flow test performed at 20 ºC. Regarding the tests performed at -7ºC, all the configurations provide quite similar results for the first 450 seconds when the HP EGR strategy is enabled. Afterwards, once the engine calibration switches from HP EGR to LP EGR, the effect of the heat recovery system is noticeable. While HP EGR is enabled (between 60 and 450 seconds), temperatures of different tests have similar trends showing that hot HP EGR gas have a much bigger impact on the intake air temperature than the recovery system. However, a bit higher intake temperature is recorded in case of heat recovery test. The reason of this bigger impact is the high enthalpy of not cooled exhaust gas recirculation. Hydrocarbons are produced at condition of lack of oxygen and low temperature as a result of the partial oxidation of the fuel, phenomena known as incomplete combustion. Under less critical ambient temperatures the EGR reduces both the peak combustion temperature and oxygen presence, producing an increase of CO and HC, in order to reduce NOx emissions. However at low temperatures the use of EGR becomes useful avoiding partial oxidation because of the higher impact of initial temperature than the oxygen dilution. This is the reason of performing no cooled HP EGR in the first stages of the cycle. From 450 seconds, HP EGR is replaced by LP EGR and the temperatures of the different tests show important reductions because of it. Between 450 and 1000 seconds the temperature differences between tests are due to the heat recovery system. Intake air temperature differences are around 25 ºC, on average. Regarding the heat recovery system test, intake temperature keeps constant due to the temperature regulation control. The aim of the thermal mangement of the WCAC is to get an accurate regulation of the intake temperature. The temperature control system acts over the valves regulating the flow circulation of the coolant to obtain a steady intake temperature indepent of the air temperature upstream of the WCAC. Between 1023 and 1488 seconds of the WLTC cycle the high load cycle part is performed. Due to the increase of load at 1200 seconds and in order to avoid intake overheating, the heat recovery system is connected to the engine coolant instead of the WCAC. Therefore, after this point the WCAC actuates as a cooler and the TFE as a standard LP EGR cooler. Between 1200 and 1400 seconds both tests show an increasingly intake temperature due to the higher engine load. After 1488 seconds, extra high engine loads are performed. Intake temperature significantly increases in 0-flow test and therefore intake temperatures are close between different tests. Finally, using the heat recovery system, similar intake temperatures are recorded between the tests performed at -7ºC and the reference (0-flow) at 20ºC. Intake temperatures evolves in a similar way for most of the WLTC except in the beginning of the cycle, where the test at 20 C presents higher temperature. This is due to the engine calibration that allows HP EGR introduction once engine coolant temperature reaches 5 C. Consequently, for 20 C test, the HP EGR is activated from the beginning of the cycle and this explains the higher temperature. Thus, the exhaust heat recovery system permits to the engine to work with intake air temperature conditions close to 20 C ambient. 7

8 Figure 9 : Intake temperature during WLTC cycle for three different configurations Figure 10 presents the engine coolant temperature evolution during the WLTC cycle at -7 C with the different configurations. With the heat recovery system, higher coolant temperature is measured, and the thermostat control temperature is reached faster, around 100 seconds earlier. This parameter indicates a quicker engine warm-up with the optimized strategy. Moreover, the heat recovery system can also be a benefit for the passenger comfort in these critical cold conditions. Effectively, the cabin heating is usually permitted once the engine coolant temperature reaches 40 C. In this case, this temperature is reached around 80 seconds earlier with the heat recovery system. 80 sec 100 sec Figure 11 : Fuel consumption and pollutant emissions of WLTC at -7 ºC 4.3. Influence of the ambient temperature on the heat recovery system in NEDC cycles. In the following section, the effect of different ambient temperatures, -7 C, 0 C and 10 C, is analyzed. In this study, heat recovery tests are compared with 0- flow tests. Results obtained in pollutant emissions for all ambient temperatures are compared in Figure 12. CO emissions improvements are remarkable with a reduction of 9% at -7 ºC and 7% at 0 ºC. Unlike the WLTC cycles the lower transient conditions of NEDC cycles show higher dependence of CO emissions on intake temperatures and no high peak of CO has been recorded. Greater reductions are obtained for unburned hydrocarbons with a reduction of 24% and 17% at -7 and 0 ºC respectively. As ambient temperature increases, the heat recovery system shows lower benefits. Once ambient temperature reaches 10 ºC, the heat recovery system does not present significant differences. In all cases fuel reduction is negligible. Figure 10 : Engine coolant temperature during WLTC cycles at -7 C Total accumulated fuel and pollutant variation of the whole WLTC cycle is depicted in Figure 11 comparing the heat recovery system test with the 0- flow reference test. Higher intake temperature improves the combustion process and therefore hydrocarbons and smoothed CO are greatly reduced, respectively of around 35% and 12%. So, the heat recovery system shows a noticeable positive performance regarding HC and smoothed CO reduction, which indicates a better combustion process. In case of fuel consumption there are not significant differences. Figure 12 : Total variation of fuel and pollutant emissions at different ambient temperatures 8

9 5. Conclusions In this paper an experimental study was carried out in order to evaluate the potential of a novel exhaust heat recovery system -TFE - in cold conditions. This system has been used initially to heat the intake air where the energy available plays a major role in pollutant reduction; but afterwards, the TFE can be used to heat the engine oil or the vehicle cabin for example, once the warm up of the engine is reached. The TFE allows recovering the maximum energy available in the exhaust gas from the engine start. In order to assess this new recovery system during tests at -7 C, a thermal strategy has been developed and tested. When the engine temperature is very low and the combustion is not optimized, all the energy is used to increase the intake air temperature. Once the intake air temperature achieves a targeted level, the thermal management strategy performs a fine tuning to keep the temperature at an optimal value. The tests results show that the applied thermal strategy permits to the engine to work close to optimal conditions (as if ambient temperature were at 20 C). Regarding impact on pollutants at -7 C, HC and CO have been significantly reduced (up to 35% reduction for HC and around 12% reduction for smoothed CO on WLTC). Their reduction thanks to the TFE strategy indicates an improvement of the combustion quality. The effect of the TFE is noticeable also in less critical conditions with higher ambient temperature. A reduction around 17% and 7% on HC and CO respectively for tests performed at 0 C on NEDC have been recorded. As the ambient temperature increases tests performed at 10 C the advantages of intake air heating are not so evident. No gains on fuel consumption were observed in these running conditions. As the main focus of the study was the pollutants reduction, no further investigation to reduce fuel consumption has been performed. The TFE system is a very simple solution and requires no external source of energy. The need of additional hardware for its implementation is very low for a modern turbocharged diesel engine, which already disposes of a water cooled charge air cooler and an LP EGR cooler. At very cold temperatures, the TFE system allows an important reduction of pollutants absolutely for free (energy recovered from exhaust gas). 6. Perspectives The impact of very low ambient temperatures together with the collateral effect of the air heating does not have a positive effect on NOx emissions. However, the combustion improvement observed thanks to the increase of the intake air temperature could be an enabler to introduce EGR earlier during the cycle and consequently, reduce the raw NOx pollutants. In order to assess this hypothesis, the calibration needs to be updated. This is not in the scope of this study, but it will be part of next research activities with a new turbocharged engine. Thus, a new study will be launched. The focus will be the diesel behavior at -7 C with the optimization of the NOx emissions as the main target, while reducing the other pollutant emissions and keeping fuel consumption at the same level as an engine running at 20 C of ambient conditions. Further optimization of the TFE and benchmarking with other heating systems will also be considered. 7. Aknowledgments This research has been partially financed by the Ministerio de Economía y Competitividad of Spain, through project IPT Investigación y desarrollo de tecnologías de EGR adaptadas a las nuevas arquitecturas y requerimientos de refrigeración en motores diésel sobrealimentados para automoción (HIREFIRE).The authors gratefully appreciate this support. Authors want to acknowledge the Apoyo para la investigación y Desarrollo (PAID) grant for doctoral studies (FPI S ). 8. References 1. A.J. Torregrosa, P. Olmeda, J. Martnal of Degraeuwe. 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10 9. Pertti Kauranen, Tuomo Elonen, Lisa Wikström, Jorma Heikkinen and Juhani Laurikko. Temperature optimisation of a diesel engine using exhaust gas heat recovery and thermal energy storage (diesel engine with thermal energy storage). Applied Thermal Engineering 30 (2010) José Manuel Luján, Héctor Climent, Benjamín Pla, Manuel Eduardo Rivas-Perea, Nicolas-Yoan François, Jose Borges-Alejo, Zoulikha Soukeur. Exhaust gas recirculation dispersion analysis using in-cylinder pressure measurements in automotive diesel engines. Applied Thermal Engineering, 2015, Volume 89, pp Payri F, Lujan J, Climent H, Pla B. Effects of the Intake Charge Distribution in HSDI Engines. SAE Technical Paper, (2010) , doi: / David C. Quiros, Seungju Yoon, Harry A. Dwyer, John F. Collins, Yifang Zhu, Tao Huai. Measuring particulate matter emissions during parked active diesel particulate filter regeneration of heavy-duty diesel trucks. Journal of Aerosol Science 73 (2014) J. Arregle, V. Bermúdez, J.R. Serrano, E. Fuentes. Procedure for engine transient cycle emissions testing in real time. Experimental Thermal and Fluid Science 30 (2006) Ramesh K. Shah, Dusan P. Sekulic. Fundamentals of Heat Exchanger Design. John Wiley & Sons. Page Glossary WLTC: Worldwide harmonized Light duty driving Test Cycle. NEDC: New European Driving Cycle. HSDI: High Speed Direct Injection. WCAC: Water Charge Air Cooler. HP EGR: High Pressure Exhaust Gas Recirculation. LP EGR: Low Pressure Exhaust Gas Recirculation. AIM: Air Intake Module. TFE: Twin Function Exchanger. 10