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Renault’s ongoing downsizing strategy is aimed at reducing the cubic capacity of its engines in order to bring down fuel consumption and CO₂ emissions, without detracting from performance.

New-generation 1.5 dCi engines. The current 1.5 dCi (type K9K) diesel is the brand’s best-selling engine with almost 900,000 units manufactured in 2009, in Valladolid (Spain) and Bursa (Turkey). It is available with several power outputs (currently from 65 to 110hp) and powers numerous Renault (from Twingo to Laguna) and Dacia models. Its simple design and low levels of friction make it particularly competitive in terms of the performance it delivers for its price.

Renault’s engineers worked particularly hard on tuning the 85hp and 105hp dCi engines to optimize CO₂ emissions without detracting from performance. Among their modifications:

• Taller ratios for all gears: the torque and response inherent in the dCi engine have enabled these changes to be introduced without affecting its performance.
• Reduced transmission friction thanks to the use of low viscosity oils.
• Specific engine-mapping aimed at reducing fuel consumption and CO₂ emissions.

Renault is in the process of introducing significant changes to this four-cylinder 1.5-liter engine. The latest evolutions will become available in 2012 and will cut CO₂ emissions by approximately 20 g/km.

The future 1.6 dCi 130 engine. When it reaches the marketplace, this all-new 1.6-liter engine will deliver a power output of 96kW (130hp). This is equivalent to a reduction in cubic capacity of 16% compared with a current 1.9-liter diesel engine of equivalent power.

The downsizing process involved shortening the piston stroke by reducing the size of the crank pin and conrod assembly. The swept volume inside the cylinder is smaller, so less fuel is consumed during each cycle. Thanks to turbocharging and the use of new technologies, performance hasn’t suffered. Downsizing alone results in a saving of 6%compared with the engine it replaces.

The forthcoming dCi 130 (R9M) will be Euro6 ready. It is covered by 15 Renault patents and will be the core C-segment engine, in addition to playing a key role in the brand’s D-segment and van ranges. It is a Renault-Nissan Alliance joint development and is due to be introduced in 2011. It will be manufactured at the Cléon plant in France.

Combined with the improvements to the forthcoming vehicles themselves (weight, aerodynamics, friction), this engine will enable CO₂ emissions to be reduced by 30 g/km, while fuel consumption will come down by more than 20% compared with the current dCi 130.

New TCe gasoline engine family. Renault introduced the 1,149cc TCe 100 for Twingo, Clio and Modus in 2007. The TCe 100 delivers the power output of a 1.4-liter powerplant and the torque of a 1.6, combined with fuel consumption of an engine of its size. It is equipped with a low inertia turbocharger and was engineered to provide standard-setting performance and fuel economy for its class. The latest Euro5-compliant version was introduced at the beginning of the year under the hood of Clio. Clio TCe 100 emits 129g of CO₂/km, which is a gain of 8 g/km over the former version.

The New Megane range saw the introduction of the new TCe 130 in 2009. This engine offers the power output of a 1.8 (130hp/96kW) and the torque of a 2.0 (190 N·m), yet its downsized 1,397cc block is more fuel efficient.

With the imminent switch to Euro 5 and Euro 6 legislation, gasoline engines are poised to become an increasingly attractive proposition, a trend anticipated by Renault’s new TCe powerplant family. Scheduled for launch in 2012, it is expected to account for 85% of Renault’s gasoline engine sales in 2015. These modular engines will have a cubic capacity of between 0.9 and 1.2 liters and will be available in three- and four-cylinder form with power outputs ranging from 65 to 85kW (90 to 115hp). A number of vehicles equipped with these engines will emit less than 100g of CO₂/km.

Technologies to reduce the CO₂ emissions of internal combustion engines

Six new technologies will significantly reduce the CO₂ emissions of Renault’s future engines in conjunction with downsizing:

• Thermal management
• Low pressure EGR (exhaust gas recirculation)
• Variable swirl technology
• Variable flow oil pump
• Triple post-injection strategy
• Stop&Start technology

Thermal management. The efficiency of a cold-running engine (up to 80°C) is penalized on two accounts:

• When the combustion chamber is cold (because the cooling fluid that surrounds it is itself cold), the combustion process is poor and incomplete, and produces a high quantity of hydrocarbons and carbon monoxide. Fuel consumption suffers, too.
• When a lubricant is cold, it is more viscous, which increases the energy required to pump it around the engine. Along with mechanical friction, this phenomenon has a negative impact on fuel consumption.

Thermal management. Click to enlarge.

Thermal management speeds up the warming of the engine. The system comprises a solenoid valve located in the cooling circuit upstream of the cylinder head and cylinder block. When the engine starts from cold, the valve is closed and prevents water from circulating around the combustion chambers. This causes the engine to warm up more quickly.

Once the optimal temperature has been reached, the valve opens and cooling reverts to the normal mode, allowing cooling fluid to flow through the cylinder block and cylinder head to control the temperature of the engine's components and ensure their reliability.

Thermal management ensures enhanced combustion and reduced friction inside the engine while it is warming up. It is estimated that this technology delivers a CO₂ emissions saving of 1%.

Lower pressure EGR (exhaust gas recirculation). The use of EGR cuts emissions by recycling exhaust gases and re-injecting them into the combustion chamber to bring down high combustion temperatures and minimize the production of oxygen, two factors which favour the production of NO_x.

Low pressure EGR. Click to enlarge.

With a conventional (high pressure) EGR, exhaust gases are recovered as they exit the combustion chamber and are still hot as they are re-injected directly into the air intake, mixed with air. Although this minimizes the production of nitrogen oxides during combustion, it raises the intake temperature and reduces turbo pressure, two factors which have a negative impact on energy efficiency.

In the case of low pressure EGR technology, the exhaust gases are recovered further downstream, once they have been through the turbine and particulate filter. They are cooled in a low pressure intercooler which enables them to be recirculated through the turbo mixed with air and thereby increase the turbo pressure.

They are then cooled by air in the turbo radiator and used for combustion a second time. This cold loop enables the recirculation rate to be increased, while at the same time lowering the temperature and pressure. Emissions of nitrogen oxides are cut more efficiently than is the case with a high pressure EGR, and engine efficiency is improved. The combustion is of a higher quality and CO2 emissions are reduced.

Low pressure EGR technology calls for an engine architecture that minimizes the distance between the catalytic converter/particulate filter and the air intake, an arrangement known as a post-turbo after-treatment system. This proximity enables:

• catalytic converters and particulate filters to function at higher temperatures and therefore more efficiently,
• the fitment of a compact and efficient low pressure EGR circuit.

Use of this technology reduces CO₂ emissions by three per cent.

Variable swirl. Click to enlarge.

Variable swirl technology. The term swirl describes the phenomenon of air rotating inside the cylinder. The swirl is produced during the induction phase and is amplified during the compression phase prior to combustion. Although swirl favors efficient combustion, its properties need to be adapted as a function of engine speed and load if performance is to be optimized.

Variable swirl technology consists in controlling the amount of swirl by means of a flap situated in the upper duct of the air intake. When the flap is in the closed position, gas flows unhindered through the ports that remain open and increases turbulence.

The air-fuel mix is consequently optimized and this reduces fuel consumption, while also minimizing the emission of CO₂ and other pollutants (nitrogen oxides and particulates) at all engine speeds.

This technology delivers CO₂ emissions savings of 0.5%.

Variable displacement oil pump. Click to enlarge.

Variable displacement oil pump. This technology allows the capacity of the oil pump to be adjusted as a function of the engine’s needs, which notably vary as a function of engine speed, to minimize the pump's energy consumption.

The capacity of a conventional oil pump is fixed and oil pressure is capped by a relief valve. Pumping the oil the engine doesn'’ need through the relief valve wastes energy, however. Variable flow pumps do away with the need for a relief valve and avoid the unnecessary consumption of energy this sort of valve requires.

The CO₂ emissions saving achieved in this way is approximately 1%.

Triple post-injection strategy. Click to enlarge.

Triple post-injection strategy. Post-injection consists in injecting fuel during the combustion phase of the four-stroke cycle. Fuel is injected into the combustion chamber at periodic intervals in the form of three very short post-injections which are controlled by the engine’s ECU.

The fuel used for the last two post-injections produces a reaction in the exhaust line, inside the catalytic converter, thanks to the prior increase in the exhaust’s temperature resulting from the combustion of the first post-injection. This enables the necessary temperature for regeneration of the particulate filter to be reached, however the engine is being used.

The triple post-injection strategy is employed to optimize the amount of the fuel used to regenerate the particulate filter and to limit dilution of fuel with the engine oil. It combats CO₂ emissions and permits extended oil change intervals.

Stop&Start technology. The system comprises a Stop&Start controller which instructs the ECU to cut the engine when three conditions are met:

• transmission in neutral,
• clutch pedal released, and
• car’s speed close to zero km/h.

When the driver presses on the clutch pedal to select first gear to pull away again, the ECU is instructed to re-start the engine, which fires up instantly, allowing the vehicle to move away. To cope with the engine’s repeated starting, the specification of the starter motor is uprated.

This technology permits a CO₂ emissions saving of 3%.

EDC automatic transmission

EDC principles. Click to enlarge.

Renault has developed a new, six-speed, automatic dual-clutch transmission called EDC (Efficient Dual Clutch) which delivers a standard of fuel consumption and CO2 emissions that marks a significant step forward compared with conventional automatic transmissions (a gain of up to 17%, i.e. a saving of approximately 30g of CO₂/km).

The EDC features a dual dry clutch combined with electric actuators; calibration is focused on minimizing fuel consumption.

The first of the two clutches looks after the odd-number gears (1^st, 3^rd and 5^th), while the second covers the even-number gears (2^nd, 4^th and 6^th), as well as reverse. The gears are carried by four shafts: two concentric primary shafts (each of which is connected to a clutch) and two secondary shafts. Gears are matched by means of synchronizers, as is the case with a manual gearbox. These synchronizers, like the clutches, are operated by electric actuators which are in turn controlled by a control unit.

This EDC is initially being applied in core-range versions of New Mégane (dCi 110 DPF). Thanks to their lower CO₂ emissions, these Méganes will be the brand’s first automatic cars to qualify for the Renault eco² signature.