C OVER STORY Innovative P owertr ains
© Volkswagen
The New 1.0-l TGI Three-cylinder Engine from Volkswagen With the new EA211 1.0-l TGI, Volkswagen developed an economical, environmentally friendly and agile power unit for the Group brands. In this article the engineers describe its development and illustrate the structural design of CNG-specific elements.
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INTRODUCTION
VOLKSWAGEN’S CNG MODELS
Volkswagen is expanding its engine portfolio and thus rounding off the bottom end of its line-up of efficient downsised power units. The flexibility of the EA211 engine range offers the best possible starting point for environmentally friendly CNG derivatives in all displacement classes. A new 1.0-l CNG engine with an output of 66 kW (90 hp) and 160 Nm of torque has been developed for use in the new modular transverse matrix (MQB)-A0 platform. Its first appli cation will be in 2017 in the new Polo TGI. The bivalent drive in the new Polo TGI offers customers the combination of running on either CNG or gasoline. The low fuel consumption (CO2 emissions of 87 g/km NEDC) and the clean combustion of CNG enable environmentally friendly and cost-effective operation. However, if CNG should be unavailable, customers still have a fully-fledged, conventional TSI at their disposal. CNG is an important factor in Volkswagen’s powertrain strategy now and in future and, in combination with electric drives, can reduce CO2 emissions on a sustainable basis. The company also places particular emphasis on renewable, biogenic generation of the energy carrier.
Volkswagen has had CNG-powered models in its model range since 2006. The Group has been forging ahead with this technology in a number of different vehicle classes for the past ten years, with the everyday usability of those vehicles paramount. All concepts are thus based on a spacesaving configuration with underfloor tanks in the vehicle floorpan that do not impinge on interior space. Volkswagen currently has several CNG models on the market. The eco up! uses a 1.0-l MPI engine with 50 kW (68 hp). It consumes 2.9 kg CNG/100 km, resulting in fuel costs of around 3 Euros/100 km (Germany 2016) [1]. The MQB-A platform features a 1.4-l TGI with 81 kW (110 hp). The turbocharged engine with 200 Nm of torque is the driving force for the Golf, Golf Estate and Caddy, [2]. Group brands Škoda, Seat and Audi also offer CNG engines, utilising Volkswagen’s efficient CNG units. Audi is also set to offer a 2.0-l TFSI as a CNG engine [3]. DEVELOPMENT TARGETS OF THE NEW 1.0-L TGI
The basis for the development was the EA211 1.0-l TSI from 2014, which was already configured to accept the components and hardware changes necessary for running on CNG [4]. The outstanding base engine has already won countless comparison tests over the last few years, leading to high expectations of the CNG derivative and correspondingly high development targets: –– CO2 emissions of less than 90 g/km –– minimal untreated emissions –– agile performance
–– bivalent set-up with no restrictions to gasoline operation –– cost-effective implementation for use by all Group brands –– the very highest quality standards and longevity. COMPACT BASE ENGINE
Volkswagen is continuing its downsizing strategy with the three-cylinder, which generates its power from a displacement of 999 cm3. The use of the EA211 engine toolkit enables cost-effective manufacture within the Group’s global production network [5]. The lightweight and compact engine is notable for a number of innovative solutions: –– pressure die-cast aluminium crankcase weighing 15 kg with cast-in iron cylinder liners –– weight-reduced crankshaft, pistons and conrods –– optimised diameters on the main and conrod bearings for reduced friction –– dual-circuit cooling for crankcase and cylinder head –– exhaust manifold integrated into cylinder head –– intake manifold with integrated charge-air cooler –– common-rail injection with a maximum pressure of 350 bar –– stepless, map-controlled oil pump –– compact layout of ancillary drives without separate mounts MODIFIED CYLINDER HEAD AND CRANK DRIVE
The crankcase is made from highstrength pressure-die-cast aluminium with cylinder liners made from GJL 250 and was carried over unchanged for the
A U T H ORS
Dr. techn. Wolfgang Demmelbauer-Ebner is Head of Gasoline Engines at Volkswagen AG in Wolfsburg (Germany).
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Dr.-Ing. Jörg Theobald is Head of Calibration EA888, EA211 I3 and Alternative Fuels at Volkswagen AG in Wolfsburg (Germany).
Dipl.-Ing. Jörg Worm is Head of Calibration Alternative Fuels at Volkswagen AG in Wolfsburg (Germany).
Stefan Becker, B. Eng. is Calibration Engineer Aalternative Fuels at Volkswagen AG in Wolfsburg (Germany).
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C OVER STORY Innovative P owertr ains
be particularly wear resistant. The conrod bearing shells were likewise adapted to the higher pressure. And fully synthetic material is used in the oil filter. COOLING CIRCUIT AND EXHAUST GAS TURBOCHARGER
FIGURE 1 Valve gear of the 1.0-l TGI (© Volkswagen)
CNG application. However, modifications were made to the cylinder head to allow for the increased demands in CNG operation, FIGURE 1. The intake and exhaust valves are fully nitrided to increase the wear resistance of the valveseat faces. Due to the high temperatures, the exhaust valves are hollow and sodium-filled. The valve stem guides on the intake side are made from high-performance brass (Diehl 470HT), which is likewise incredibly hard and wear resistant. The valve-seat inserts are made from sintered and copper-infiltrated steel (AR20D).
On the intake and exhaust valves, the closing ramps are flattened to 0.17 mm of valve lift to enable the valves to close more slowly and thereby minimise wear. The cylinder head gasket has a three-layer design. The ignition coils deliver a higher ignition voltage during CNG combustion. Due to the high peak pressure of up to 115 bar in CNG operation, it was necessary to make some design modifications to the crank drive, FIGURE 2. In CNG operation, the higher gas forces subject the piston rings, especially the first ring, to increased friction with the cylinder liner, which is why they were designed to
FIGURE 2 Base drive of the 1.0-l TGI (© Volkswagen)
The overall higher temperature level is already accounted for in the modular base concept of the EA211 engine. Only the inclusion of the gas-pressure regulator resulted in minor modifications to the cooling system. The newly developed single-scroll turbocharger for the 1.0-l TGI was matched to the exhaust manifold integrated into the cylinder head. The turbocharger housing is made from cast austenitic steel, while the bearing casing is water cooled. The turbine rotor is made from nickel-based alloy MAR-M 246 and is designed to withstand the high mechanical and thermal loads associated with exhaust temperatures of up to 1050 °C. As in the 1.0-l TSI, the wastegate actuator is electrically operated. OPTIMISED CATALY TIC CONVERTER AND HEATED LAMBDA PROBES
Methane is an extremely stable molecule with a conversion temperature around 50 to 100 K higher than that of gasoline. The catalytic converter used in the 1.0-l TGI is geometrically the same as this one in the 1.0-l TSI. However, the coating and depletion was adapted for methane conversion to achieve the optimum methane conversion rate. One major prerequisite for the best possible emissions characteristics during warm-up and for the use of the lambda split process during this phase is a lambda probe with no dew-point end, FIGURE 3. It is electrically heated to reach its control status no later than around 10 s after engine start. Technically, this is achieved through a dual protective pipe and optimised coating of the sensor element to ensure that moisture in the exhaust cannot damage the ceramic part of the element. HIGHLY INTEGRATIVE ENGINE CONTROL
The engine control for the 1.0-l TGI is notable for a high level of functional integration. This includes the TSI operating
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procedure in gasoline-powered mode, the MPI operating procedure in CNG mode and management of the gas components and electronic gas-pressure regulator. A pressure/temperature sensor located at the entrance to the rail is used to regulate CNG mass flow. A high-pressure sensor at the entrance to the gas-pressure regulator measures the fill level of the gas tank. The engine control unit uses the lambda probe to recognise the different gas qualities of low-calorific (L) and high-calorific (H) gas. L-gas has a lower methane and therefore energy content than H-gas. The control unit adapts the injection times for both sorts accordingly. ELECTRONIC GASPRESSURE REGULATOR
The electronic gas-pressure regulator, FIGURE 4, lowers the pressure in two stages from a maximum of 260 bar in the tanks to the 5 to 9 bar (absolute) in the low-pressure system. In the first stage, mechanical throttling reduces the pressure to around 20 bar, while the second stage uses electronic regulation via a solenoid valve to reach operating pressure. Integrated into the mechanical pressure-reduction stage is a damping filter with a metal core. This structure prevents the formation of standing waves, which could lead to annoying whistling
FIGURE 3 Exhaust turbocharger and catalytic converter of the 1.0-l TGI (© Volkswagen)
sounds. Reducing the pressure in the pressure regulator leads to extreme cooling of the natural gas. In the 1.0-l TGI, the regulator is incorporated into the coolant loop, which warms it up. This solution prevents unacceptable cooling of the components and ensures the gas exit temperature remains above -40 °C at all times. SPECIAL MOUNTING POINTS FOR GAS RAIL
The intake manifold has special mounting points for the stainless-steel gas rail.
The gas injection valves are inserted into the inlet ports. Ball-flange connectors will be used in future for all connections in the line between the gas bottles and the rail. They have benefits compared with clamping screw attachments and are also more cost-effective to use. OPERATING PRINCIPLES AND OPERATING MODE-STRATEGY
In everyday operation, the new 1.0-l TGI must always be able to switch as required between the two operating modes, natural gas and gasoline. The torque-neutral
FIGURE 4 Gas-specific components for the 1.0-l TGI (© Volkswagen)
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C OVER STORY Innovative P owertr ains
TABELLE 1 Comparison of the main characteristics of CNG/gasoline and the effects in CNG operation (© Volkswagen) –
Methane CH4
Super-grade gasoline
Effect
Boiling point
- 162 °C
25-210 °C
– CNG always gaseous – No lubrication – No phase transition and thus no evaporation cooling
Energy content
13.9 kWh/kg
8.9 kWh/kg
Density
0.73 kg/m³
720-770 kg/m³
– Storage under pressure required – Lower range
Ignition temperature
650 °C
400 °C
– – – –
95
– Efficiency-optimised ignition angle possible across entire map range – Increased peak pressures and combustion chamber temperatures, resulting in increased combustion chamber loads
Octane figure
130
–
Increased ignition voltage required Modification of ignition coil and spark plugs Increased catalyst conversion temperature Modification of coating
of gasoline has been consumed to flush out the non-return high-pressure fuel pump. If the vehicle was driven in gasoline mode prior to filling up with CNG, the system will switch immediately to CNG mode as soon as lambda regulation starts as the fuel pump was already flushed during previous operation in gasoline mode. The switch from gasoline to CNG operation takes less than 1 s. The gas quality (low or high) is then determined to ensure the mixture is correctly managed. Once the adaptation is complete, the 1.0-l TGI starts up in gas mode on every subsequent start above -10 °C until the next refuelling procedure. CATALY TIC CONVERTER – A CHALLENGE WITH CNG
transition represents the greatest challenge in the engine application. There is a system-based dynamic disadvantage in CNG operation because, for one thing, the exhaust gas temperatures are below those of gasoline operation under almost all conditions and, for another, the air delivery rate is 15 % lower than in gasoline mode because of the gas injection into the intake manifold, TABLE 1. To achieve the same full-load curve as in gasoline operation, the maximum charge pressure in CNG operation is raised by 0.3 to 2.3 bar (absolute) and ignition timing advanced. The small turbocharger also aids the rapid build-up of charge pressure.
As long as there is CNG in the tanks, the TGI starts and runs in gas mode at coolant temperatures above -10 °C. At lower temperatures, it starts up in gasoline mode. In this case, the gas rail is first evacuated by opening the injection valves slightly while the gas-pressure regulator is closed. Afterwards, the injection valves are electrically heated until they have reached their operating temperature and open safely. Operation then switches to CNG mode. The engine also runs initially on gasoline the first time it is started after filling up with CNG. The switch to gas takes place as soon as lambda regulation has been activated and at least 140 ml
FIGURE 5 Comparison of λ-split versus ignition-angle retardation (© Volkswagen)
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To achieve the lowest possible emissions, it is necessary to heat up the catalyst to light-off as quickly as possible and to maintain it above the conversion temperature during low engine load. This represents a particular challenge with CNG concepts as the conversion temperature of methane is around 100 K above that of gasoline, while the exhaust temperature is lower than in gasoline mode due to the consumption-optimised ignition angle. A conventional cat-heating process is activated following cold start. The required ignition-angle retardation and the increased engine speed result in lower operating efficiency and thus higher CO2 emissions. The aim is to leave this operating mode as quickly as possible and return to efficiencyoptimised operation. To achieve this, a lambda split process has been incorporated into a three-cylinder for the first time, with almost zero negative impact on efficiency, FIGURE 5. This means that two cylinders run on a rich mixture and one on a lean mixture. The lambda sum for all cylinders remains 1. The rich cylinders form CO, which is converted by the catalytic converter in an exothermic reaction. The conversion temperature of CO is significantly less than that of methane. When the CO conversion temperature is reached during conventional cat warm-up, the system switches to lambda split. This function is also activated in low partial load before the temperature drops below that of methane conversion.
The 1.0-l TGI delivers an output of 66 kW (90 hp) in both CNG and gasoline operation. Its maximum torque of 160 Nm is constantly available from 1900 to 3500 rpm, FIGURE 7. The Polo TGI accelerates from 0 to 100 km/h in 11.5 s and reaches a top speed of 184 km/h. Power transmission is via a five-speed manual gearbox. When running on CNG, the average consumption in the NEDC is 3.2 kg/100 km, which equates to CO2 emissions of 87 g/km. The range is 390 km. It has an additional range in gasoline mode of around 930 km, resulting in a total range of 1320 km.
FIGURE 6 Layout of the gas tanks of the Polo TGI (© Volkswagen)
SUMMARY MAINTENANCE-FREE GAS TANKS IN THE NEW POLO
The flexibility of the MQB enables special packaging in the middle and rear of the vehicle floorpan. Despite the addition of two cylindrical pressure vessels with a combined volume of 75 l in addition to the standard gasoline tank, the volume of the luggage compartment is not affected. The restraint system for the highstrength steel vessels, FIGURE 6, secures them against collision and misuse and consists of lightweight glass-fibre-reinforced thermoplastic mats pressed into shape. For maximum corrosion protection, they are sand-blasted then galvanised, coated with an epoxy primer and finally with a powder enamel topcoat. The gas bottles
are maintenance-free and, assuming corresponding compliance with the stipulated four-year inspection intervals, can remain installed for the entire vehicle life. LOW FUEL CONSUMPTION AND HIGH RANGE
The driver of the Polo TGI can see the operating mode, gas quality, fuel level, current and average fuel consumption and remaining range in the dashboard multifunction display. In addition to the gasoline gauge, a further fuel guage provides information on the amount of CNG in the tanks. The CNG fill point is next to the gasoline fill point beneath the fuel cap. A zero-maintenance particulate filter protects the system from impurities.
With the new 1.0-l TGI, Volkswagen is providing the Group brands with an economical, environmentally friendly and agile power unit. The inclusion of the MQB-A0 platform as a new vehicle class is an impressive demonstration of the importance of natural-gas drive for the future of the Volkswagen brand. Attractive pricing, low fuel consumption, minimal emissions and competitive performance combined with low operation costs offer real and noticeable customer benefits. The Polo TGI plays an important role in Volkswagen’s CNG strategy. It also accommodates the use of sustainably generated biomethane, which is almost climate-neutral in well-to-wheel reckoning. Against this backdrop, CNG vehicles can be highly complementary to BEV and PHEV concepts on the road to CO2-neutral mobility.
FIGURE 7 Full load curve of the 1.0-l TGI (© Volkswagen) REFERENCES [1] Neußer, H.-J.; Szengel, R.; Kirsch, U.; Worm, J.: The new three-cylinder CNG engine in the Volksw agen eco up!. 24 th International AVL Conference “Engine & Environment”, 2012 [2] Mendl, G.; Mangold, R.; Rosenberger, S.; Langa, Z.; Czuczor, B.: The new Audi 2.0 l g-tron – a further step towards the sustainable mobility of the future. 38 th International Vienna Motor Symposium, 2017 [3] Eichler, F.; Middendorf, H.; Helbing, C.; Hentschel, L.; Scherf, J.; Wendt, W.: The new 1.0-l three-cylinder TSI. 35 th International Vienna Motor Symposium, 2014 [4] Eichler, F.; Demmelbauer-Ebner, W.; Persigehl, K.; Wendt, W.: The 1.0 l 3-cylinder TSI engine in Volkswagen’s modular system. In: MTZworldwide 75 (2014), Nr. 11, pp. 18-23 [5] Eichler, F.; Szengel, R.; Helbing, C.; Worm, J.: The new EA211 1.4 l TSI CNG. 22nd Aachen Vehicle and Motor Colloquium, Aachen (Germany), 2013
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