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THE NEW 1.6-L DIESEL ENGINE FROM HONDA Honda developed the third generation diesel engine to balance further CO2 reductions with dynamic performance. This development focused on downsizing the engine and succeeded in developing a compact, lightweight and high-efficiency 1.6-l four-cylinder turbocharged diesel engine. The Honda Civic equipped with this engine achieves a CO2 emission of 94 g/km (3.6 l/100 km) in the NEDC and improves fuel economy by 14.5 % as compared to the second generation 2.2-l diesel engine of Honda.
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AUTHORS
NORITSUGU IKEGAMI is Chief Engineer at the Automotive R&D Center of Honda R&D Co., Ltd in Tochigi (Japan). He is the project leader of the development project of i-DTEC 1.6L and responsible for the market and development strategies of Honda’s diesel engines.
SEIJI MORI is Chief Engineer at the Automotive R&D Center of Honda R&D Co., Ltd in Tochigi (Japan). He is the assistant project leader of the development project of i-DTEC 1.6L and responsible for engine hardware design in the project.
TORU YANO is Chief Engineer at the Automotive R&D Center of Honda R&D Co., Ltd in Tochigi (Japan). He is the assistant project leader of the development project of i-DTEC 1.6L and responsible for engine and vehicle calibration in the project.
TETSUYA MIYAKE is Chief Engineer at Honda R&D Co., Ltd in Gurgaon (India). He is the assistant project leader of 2013 model year CIVIC equipped with i-DTEC 1.6L and responsible for its diesel powertrain.
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BACKGROUND
In view of the ongoing process of global warming, Honda has set itself the target of cutting the CO2 (carbon dioxide) emission of all its products sold worldwide by 30 % by the year 2020 compared to the level in 2000. In order to avoid any impairment in driving enjoyment while nevertheless minimising CO2 emission, Honda has developed what it calls its “Earth Dreams Technology”, a new generation of powertrain technologies aimed at improving the efficiency of internal combustion engines and transmissions as well as further developing electrification technologies. The 1.6-l turbocharged four-cylinder inline diesel engine, which was launched at the end of 2012 (under the name i-DTEC 1.6L) [1], is the first representative of this Earth Dreams Technology in Europe. Honda launched its first generation of diesel engines [2, 3], a turbocharged 2.2-l four-cylinder inline diesel engine, in 2004. This first generation diesel engine was highly acclaimed for its low fuel consumption and low engine noise. In the next step, the engine was further developed by optimisation, in particular in the field of engine friction, and through further measures to improve fuel efficiency. This second-generation diesel engine [4, 5] was launched in 2008 as i-DTEC 2.2L. Greater environmental awareness among the car-buying public is currently resulting in a very strong increase in demand for compact vehicles. Diesel engines require a very robust structure for the engine block due to their high cylinder pressures, as well as a large-sized exhaust aftertreatment system. Both of these factors make the diesel engine heavier and bigger than gasoline engines with the same displacement. In frontengined vehicles, the weight of the engine has a major influence on the vehicle’s dynamic properties, and it goes without saying that a lower engine weight is beneficial. A further aspect is that more and more vehicles in the compact car segment have been fitted with diesel engines in recent years, thus further emphasising the need for a compact engine particularly in this vehicle segment. For this reason, Honda has developed a new third-generation diesel engine aimed at providing the opportunity for downsizing and further reductions in fuel consumption. The Honda Civic i-DTEC 1.6L (C-segment vehicle) emits 94 g of CO2/km (3.6 l/100 km) in the NEDC, thus improving its fuel consumption by 14.5 % compared to a Civic with the 2.2 l diesel engine. In the following, the concept of the new 1.6 l engine as well as the technologies applied and their effects are described. ENGINE CONCEPT
The concept of the 1.6-l diesel engine is the simultaneous fulfilment of the following requirements: high efficiency (CO2 reduction), low weight and compact dimensions. To achieve this, Honda has downsized the engine and reduced its cubic capacity from 2.2-l to 1.6-l. However, downsizing alone is not sufficient to fulfil all of the requirements listed above at a high level. Therefore, the three technology groups listed below and shown in ❶ were focused on and applied to the i-DTEC 1.6L: : downsizing and weight reduction on the engine block : technology to minimise friction losses : low-emission and high-efficiency combustion.
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Downsized and lightweight engine block Low-friction technology Open deck cylinder block High-stiffness cylinder head
Lightweight and low-friction piston New material crankshaft Rapid warm-up cooling system
LP-EGR Multi-hole and small-diameter injector Optimised combustion chamber Low-emission and high-efficiency combustion
The new cylinder block is aimed at fulfilling the requirements low weight and compact dimensions. It comprises an open deck layout and a high-stiffness cylinder head. The second technology group has the aim of improving fuel efficiency by reducing mechanical friction losses. It mainly consists of the three technologies lightweight and low-friction pistons, a crankshaft made of a new material and a cooling system with rapid warm-up properties. These technologies have a decisive influence on high efficiency. As the first two technologies have the effect of reducing the weight of the pistons and crankshaft, they also contribute to lowering the weight. The third technology group – lowemission and high-efficiency combustion – is aimed at fulfilling the high efficiency and is made up of the following measures: multi-hole injector nozzles with a small nozzle hole diameter, an optimised combustion chamber and a low-pressure exhaust gas recirculation (LP-EGR). On the new diesel engine, LP-EGR was used both to improve thermal efficiency and to reduce engine-out NOx emissions. Downsizing usually involves reducing the cylinder bore, which makes it difficult to maintain optimum combustion and therefore results in deterioration in combustion efficiency. For that reason, it was essential to optimise the injector nozzles and the combustion chamber. The 1.6-l diesel makes efficient use of the aforementioned technologies and ultimately fulfils the three requirements at a high level.
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❶ Technical groups applied to the new 1.6-l diesel engine
DOWNSIZING AND WEIGHT REDUCTION ON THE ENGINE BLOCK
The previous engine with 2.2-l displacement was manufactured using so-called Advanced Semi-solid Casting Technology (ASCT) and had a closed deck aluminium cylinder block. By contrast, the 1.6-l cylinder block was designed with an open
deck layout, and its manufacturing process was also changed from ASCT to HPDC (High Pressure Die-Casting) in order to achieve further weight reductions on the block. ❷ shows the engine design comparison between the 2.2- and 1.6-l diesel engines. Suppressing the vertical motion of the crimps around the bore on the cylinder head gasket is an important part of the requirements to be fulfilled in open-deck cylinder blocks. For this reason, the geometry and stiffness of individual components were optimised with a minimum increase in weight in order to ultimately increase the dimensional stability of the bore and the stiffness of the cylinder head. Furthermore, the placement and shape of the ribs were optimised using Finite Element Methods (FEM) and endurance strength analyses in order to achieve further weight savings in this area too. In addition, the conventional ladder frame design for the crankshaft bearing mounts was changed to a design with independent bearing caps. In independent bearing caps, there is a risk of friction wear between the cylinder block and the bearing, and this problem was counteracted by optimising the stiffness of the indivi-
❷ Comparison of engine head and block structure of the 2.2- (left) and 1.6-l engine (right)
dual areas and their shapes with the aid of non-linear FEM. These optimisation measures achieved a weight reduction of 11.6 kg (-33 %) for the new engine block unit compared to the 2.2-l engine block unit. HIGH-STIFFNESS CYLINDER HEAD
Guaranteeing the sealing effect of the cylinder head gasket is essentially important for the diesel engine with its high gas pressures. In order to meet this requirement, a design in which the camshaft journals are integrated into the cylinder head was chosen for the new 1.6-l engine, as shown in ②. Furthermore, the depth of the water jacket in the cylinder block, the depth of the tapped hole for the cylinder head screws, the wall thickness of the cylinder bore, the valve depth and the height of the cylinder head were all optimised using FEM based on an analysis of the surface pressure of the cylinder head gasket. This ensured sufficient sealing with a low tightening torque. Due to the application of these measures in particular, the overall stiffness of the cylinder head was increased, thus making the use of an open deck cylinder block possible in the first place. TECHNOLOGY TO MINIMISE FRICTION
Approximately 55 % of the friction losses in an engine are caused by mechanical friction, approximately half of which is caused by the cyclic movement of the piston-crank mechanism of an engine. For this reason, lightweight and low-friction pistons were developed. As shown in ❸, the skirt area of the pistons on the
❸ Skirt area reduction of a piston: conventional (left) and 1.6-l engine (right)
new 1.6-l diesel engine was reduced by 26 %, while at the same time guaranteeing the oil inlet and outlet openings of the cooling ducts and the manufacturing tolerances. As a rule, a reduction in the piston skirt area results in disadvantages with regard to wear behaviour and noise emission. This was counteracted by optimising the shape of the skirt and its strength without increasing friction. This new piston not only reduces piston friction by 5 % but also the weight of the piston itself. In order to minimise friction losses at the crankshaft, it is effective to reduce the journal and bearing diameter of the crankshaft. However, a downsized engine is required to generate torque equivalent to that of a conventional engine, and for that reason, the diameter of the crankshaft and journals cannot be reduced without having an impact on strength. For this reason, a newly developed nitriding process was used, in which fine molecular molybdenum vanadium (Mo-V) is diffused into the material, achieving a 45 % increase in fatigue strength compared to conventional mate-
rial. In addition, this new hardening process also helps to reduce the weight of the crankshaft. COOLING SYSTEM FOR RAPID WARM-UP
In the warm-up phase after an engine starting, the viscosity of the oil is very high due to the low temperature, with the result that friction inside the engine is high. Therefore, shortening the engine’s warm-up period could reduce the energy loss caused by engine friction and improve fuel consumption. ❹ shows the newly developed thermostat, which enables the new engine to reach its operating temperature more rapidly. In this thermostat, a flow straightener delivers the warm water leaving from the engine to the wax that controls the opening of the thermostat without mixing with cold water from the radiator. This avoids large overshoots and fluctuations of the control temperature, and can significantly improve the control accuracy of coolant temperature compared to a conventional thermostat. This has major advantages for fuel consumption especially in the part load range, in which the engine is controlled to a higher temperature level, thus reducing engine friction. In the NEDC, the new thermostat shortened the warm-up phase by 5 s and resulted in an overall reduction in CO2 emission by 3.9 g/km due to lower engine friction and reduced thermal losses. LOW-EMISSION AND HIGHEFFICIENCY COMBUSTION
❹ Thermostat structure comparison: conventional (left) and 1.6-l engine (right) 03I2014
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Downsizing the engine displacement from 2.2- to 1.6-l has been achieved by reducing the diameter of the cylinder bore. However, a small bore increases
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soot formation due to the fact that the fuel spray impacts the combustion chamber wall without combustion. It was therefore necessary to reduce the penetration of the fuel spray into the combustion chamber. An effective method is to reduce the nozzle hole diameter of the multihole injector and to increase the number of holes. For that reason, the seven-hole injector with a nozzle hole diameter of 0.123 mm in the 2.2-l engine was changed to a eight-hole injector with a nozzle hole diameter of 0.114 mm in the 1.6-l engine. The new injector enabled soot formation to be reduced by approximately 45 % in steady-state operation at an engine speed of 2500 rpm, an indicated mean effective pressure of IMEP = 1130 kPa and an air requirement of A/F = 20.
❺ Distribution of equivalence ratio in combustion chamber: conventional cavity (top) and cavity of 1.6-l engine (bottom)
OPTIMISED COMBUSTION CHAMBER
The increase in soot formation in a small cylinder bore is caused by the local shift in the equivalence ratio towards a rich mixture, which is due to the impact of the fuel jet against the combustion chamber wall and the decrease in the volume of a combustion cavity. For this reason, as mentioned above, the fuel penetration was reduced in the new 1.6-l engine and at the same time the cavity shape was optimised with the aim of suppressing those areas with a rich equivalence ratio in the combustion chamber. ❺ shows a comparison between the distribution of the equivalence ratio in the combustion chamber in a conventional cavity (top) and that of the new engine (bottom). Whereas the connection from the cavity dome to the cavity floor is a straight line in the 2.2-l engine,
the 1.6-l engine uses a curved cavity shape. This cavity shape ensures a sufficiently high swirl motion of the airflow in the combustion chamber, resulting in a significant reduction in areas with a rich air-fuel equivalence ratio in the combustion chamber. This optimisation of the cavity shape enabled soot formation to be reduced by approximately
Air cleaner Intake throttle Intercooler Compressor Intake shutter valve
LP-EGR valve
HP-EGR valve
EGR cooler Turbine
DOC
DPF
HP-EGR LP-EGR
❻ Intake and exhaust system
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20 % at the operating point of 2250 rpm and engine torque of 135 Nm. LOW-PRESSURE EXHAUST GAS RECIRCULATION
The new downsizing engine is equipped with low-pressure exhaust gas recirculation (LP-EGR) in addition to the conventional high-pressure exhaust gas recirculation (HP-EGR) system, ❻. In LP-EGR, the exhaust gas is drawn off downstream of the turbine. As a result, the exhaust volume flow through the turbine does not decrease as the EGR rate rises. This means that the higher exhaust flow through the turbine increases the supercharging effect, while the introduction of EGR above the compressor increases the volume flow at the compressor and the pressure ratio is shifted towards higher pressures, thus improving the efficiency of the compressor, as shown in ❼. Furthermore, in small exhaust turbochargers with a low volume flow rate in the compressor, the efficiency of the
Downsize compressor
4.5
Pressure ratio [-]
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Actual area -
Area
+
Differential pressure sensor
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P dV RT
LP-EGR 2.5
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Actual fresh air Actual LP-EGR mass
10.0 12.5 15.0 17.5
Corrected flow [lbs/min] ❼ Efficiency map of the compressor (engine speed = 2000 rpm, BMEP = 900 kPa [1 lbs/min = 0.45 kg/min])
compressor is additionally improved. For this reason, LP-EGR ultimately achieves an improvement in the overall mechanical efficiency of the engine due to the increase in efficiency of the turbocharger. During driving, the use of LP-EGR reduces the emission of CO2 by 3.5 g/km in the NEDC compared to the use of HP-EGR alone. Therefore, LP-EGR is not primarily used to reduce nitrogen oxides (NOx) but rather to improve mechanical efficiency. LP-EGR does, however, have a disadvantage in the control accuracy of the recirculated exhaust gas in a transient operating state. As can be seen in ⑥, the control distance for LP-EGR is much
-
-
+
+
+
+
-
-
Target area
Area
+
Position
+ Nozzle equation
+
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Target HP-EGR valve position
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❽ Cooperative model-based controller for LP-EGR and HP-EGR (PI: Proportional Integral)
longer than that of HP-EGR. In LP-EGR, this results in a time delay between the desired value and the actual value during the control process. For that reason, a model-based controller [6] for cooperative control between HP- and LP-EGR was developed for the new engine, ❽. In the event of a delay in the desired value from the LP-EGR in transient operation, the model based controller compensates for the lack of exhaust gas volume flow from the low-pressure EGR by using the high-pressure EGR. This guarantees sufficient NOx reduction even in transient operation while at the same time maximising the fuel consumption benefit.
PERFORMANCE AND COMPETITORS
The torque and power output data of the new Honda diesel engine are a maximum torque of 300 Nm at 2000 rpm and maximum output of 88 kW at 4000 rpm. As mentioned above, the Honda Civic i-DTEC 1.6L achieves CO2 emission of 94 g/km in the NEDC. ❾ shows several of the Civic’s competitor vehicles plotted on a graph of CO2 emission in the NEDC over acceleration performance from 0-100 km/h. One can see that the Civic is even above the balance curve of acceleration and CO2 emission. As a result, it can be seen as one of the most balanced
300 Diesel 250
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115 110 105 100
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Acceleration performance 0-100 km/h [s] ❾ Comparison of acceleration performance and CO2 emission balance (green dots: competitors) 03I2014
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❿ Comparison of the 1.6-l Honda diesel engine and other series-production engines regarding engine weight and torque (green and blue dots: competitors)
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vehicles in its class in terms of fuel efficiency and dynamics. ❿ shows a comparison between the 1.6-l Honda diesel engine and other series-production engines, plotted on a graph of engine weight over torque. As described in detail in this report, numerous weight-saving measures have been introduced on the new Honda engine. As a result, it is the lightest engine compared to other engines, including gasoline engines with equivalent torque. Furthermore, the downsizing concept has made it possible to reduce the length of the engine by 100 mm and the width by 50 mm compared to the 2.2-l engine, thus greatly improving the possibilities of installing it, especially into vehicles of the compact class. SUMMARY
In order to exploit the excellent fuel-efficiency benefits of a diesel engine even in compact-segment vehicles, Honda has made use of a downsizing concept and
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developed an all-new 1.6-l diesel engine. The following three technology groups were applied: : downsizing and weight reduction on the engine block : technology to minimise friction : low-emission and high-efficiency combustion. These measures have made a lightweight and compact engine with outstanding fuel-efficiency properties. The result is CO2 emission in the NEDC of 94 g/km in a Civic, thus making it one of the cars that offer the best balance between fuel efficiency and vehicle dynamics. REFERENCES [1] Yamano, J.; Ikoma, K.; Matsui, R.; Ikegami, N.; Mori S.; Yano, T.: The New “Earth Dreams Technology i-DTEC” 1.6 L Diesel Engine from Honda. 34 th Vienna Motor Symposium, 2013 [2] Nagahiro, K.; Abe, T.; Okawara, K.; Yamazaki, M.; Hara, I.: Die Entwicklung der Dieselmotorreihe i-CTDi von Honda. In MTZ (66) 2005, No. 7-8, pp 546-550 [3] Nagahiro, K.; Aoki, T.; Minami, H.; Kikuchi, M.; Hosogai, S.: Development of New 2.2-liter Turbocharged Diesel Engine for the EURO-IV Standards. SAE Paper 2004-01-1316, 2004
[4] Matsui, R.; Shimoyama, K.; Nonaka, S.; Chiba, I.; Hidaka, S.: Development of High-performance Diesel Engine Compliant with Euro-V. SAE Paper 2008-01-1198, 2008 [5] Murata, Y.; Tajiri, K.; Sasaki, Y.; Fukushima, H.; Ueno, T.; Koide, S.: Development of the New 2.2l Fuel-Efficient Diesel Engine for Honda Civic. 21st Aachen Colloquium Automobile and Engine Technology, 2012 [6] Nishio, Y.; Hasegawa, M.; Tsutsumi, K.; Goto, J.; Iizuka, N.: Development of New Generation 1.6L Diesel Engine. 11th International Conference on Engines and Vehicles (ICE2013), SAE Paper 201324-0133, 2013
THANKS Masami Ohshima and Masaki Kanehiro, both Automotive R&D Center of the Honda R&D Co., Ltd in Tochigi (Japan), have also collaborated in the writing of the article.
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