The GTD has been the long-distance express vehicle in the Golf programme for 31 years now – combining the performance of a sports car with the fuel economy of a sub-compact car in a fascinating way. Volkswagen is now launching a new GTD on the market that is based on the seventh generation Golf. It is the most powerful Golf turbo-diesel ever with a nominal power that has been boosted by 14 to 184 PS (or 135 kW, at 3,500 to 4,000 rpm). This "GTI among the diesels" is driven by an entirely new four-cylinder TDI of the EA288 series – a transverse mounted, charged two-litre engine with common rail direct injection. Its maximum torque is a substantial 380 Nm – a gain of 30 Nm compared to the previous model – which is available over a broad rev range between 1,750 and 3,250 rpm. The TDI has a compression ratio of 15.8:1.
Sports car performance. The new engine spurs the Golf GTD on to extremely sporty driving performance. It also lowers the weight-to-power ratio to 7.5 kg/PS (including driver) and sprints the base version of the Golf GTD, which is a lightweight 1,377 kg, from 0 to 100 km/h in 7.5 seconds; the Volkswagen also sprints from 80 to 120 km/h in a short 7.5 seconds (in fifth gear) and reaches a top speed of 230 km/h. By comparison, the same data for the predecessor is: 8.1 seconds (0-100 km/h), 8.0 seconds (80-120 km/h) and 222 km/h.
Fuel economy of a compact. With a 6-speed gearbox, the TDI - that is equipped with a stop/start system as standard - has fuel consumption of just 4.2 l/100 km (CO2 emissions: 109 g/km). Compared to the previous model, this represents a 0.9 litre reduction in fuel consumption per 100 km, which equates to a respectable 25 g/km CO2 reduction. As an option, the Volkswagen also offers the Golf GTD in combination with a 6-speed dual-clutch gearbox (DSG) – here too, at 4.5 l/100 km (CO2: 119 g/km) the diesel exhibits the fuel consumption of a highly efficient car (previous model: 5.4 l/100 km).
A short retrospective illustrates just how efficient the new 184 PS Golf is: the first generation of the Golf BlueMotion made its debut in 2007. The 77 kW / 105 PS Golf consumed 4.5 l/100 km; at the time this value was celebrated as sensational. In the new GTD, Volkswagen is now launching a Golf on the market that has 79 PS more power and is 40 km/h faster, yet it consumes 0.3 litre less fuel. That is measurable progress.
Technology of the new TDI
EA288 engine series. As noted, the TDI of the Golf GTD comes from the new EA288 four-cylinder diesel engine series which covers engine displacements ranging from 1.6 to 2.0 litres. In the new Golf GTD, the most powerful extension level of the 2.0 TDI is used. Aboard the sporty Golf, the efficient engine conforms to the challenging Euro-6 emissions standard. In its design, the only parameter the new TDI engine series shares with the previous engine is its cylinder spacing (88 mm). To handle the much greater complexity of engine functions, Volkswagen also developed an entirely new software for the engine controller. The most important new features of the GTD engine include its variable valve timing (VVT), dual-loop exhaust gas recirculation (EGR), intercooler integrated in the induction pipe, the common rail system that now operates at 2,000 bar instead of 1,800 bar and a turbocharger designed for the higher power level.
Variable valve timing. Variable valve timing with a camshaft adjuster is the most important component for reducing internal engine emissions. The approach implemented in the GTD engine enables such benefits as highly effective compression during cold start and the hot running phase, low-emissions combustion with very good NOx and particulate values and sustained strong chamber filling up to the full load range.
Dual-loop EGR system. The new dual-loop EGR system assumes high importance in attaining the lowest emissions. It consists of a cooled low-pressure EGR system (LP-EGR) on the exhaust side and an uncooled high-pressure EGR system (HP-EGR) on the induction side. Background: The stringent requirements of the Euro-6 emissions standard make it essential to attain further significant reductions in emissions immediately after a cold start. The primary solution is to utilise an uncooled high-pressure EGR; its higher induction air temperature improves combustion behaviour and thereby ensures higher exhaust temperatures for accelerated response of the catalytic converter. The results: low engine-out HC emissions (hydrocarbons) with low NOx values.
In addition, mixing uncooled exhaust gas (HP-EGR) during low-rev driving prevents cooling of emissions control processes that can even occur with a hot engine. Meanwhile, the low-pressure EGR system plays out its advantages in the usual driving ranges up to the full-load range to assure highly effective NOx reduction even at higher load demands.
The HP-EGR loop is supplied via an integrated flange on the exhaust manifold; it routes the exhaust gas via a gas outlet in the cylinder head to the water-cooled HP-EGR valve, which is mounted on the outlet box of the intercooler integrated in the induction pipe. This direct component layout eliminates the EGR lines that were needed in the previous model. This arrangement also enables faster reactions to target value changes in the part-load range.
Common rail injection. A common rail system from Bosch is used in the new Golf GTD engine. The system pressure that is supplied here via a high-pressure pump was increased by 200 bar to 2,000 bar compared to the Euro-5 engines of the model series. Among other things, this permitted shortening the injection time. And in turn this allowed more flexible configuration of the combustion process. The injection quantities are metered by further developed injectors with solenoid valves; compared to the previous injectors, they are characterised by considerably faster response. An additional fuel volume in the form of a mini-rail in the injector body also minimises pressure waves on the nozzle needles, which has positive effects on the stability of the injection volumes. The nozzle needles used here also reduce CO2 and HC emissions. Last but not least, just like the improved injector the nozzle optimises EGR compatibility; and that further reduces NOx emissions.
Complex emissions control. To assure conformance to the Euro-6 emissions standard, a NOx storage catalytic converter was placed upstream of the diesel particulate filter in the Golf GTD. The exhaust system also has two lambda sensors; one sensor handles control of the reduced-air operating modes of the NOx storage catalytic converter. It also supplies the input variable for the model stored in the engine controller for determining the engine's NOx and soot emissions. The second lambda sensor is used to determine the load state and aging state of the NOx storage catalytic converter. Meanwhile, three temperature sensors also integrated in the exhaust system supply the input variables for controlling the regeneration operating modes and exhaust gas temperatures.
Balancer shafts for the GTD engine. The new diesel in the Golf GTD is not only very low in emissions, fuel-efficient and torque-strong; it is also very smooth running. This is achieved in part by the use of two balancer shafts with anti-friction bearings. They eliminate system-induced free inertial forces that occur in piston engines.