As you will have noticed, the R9M represents ‘downsizing’. It features a ‘square’ architecture, plus a substantial number of patents: more than 30. A stop-start system is fitted, and regenerative charging is deployed for the battery — the alternator usually works only on overrun. Other notable features include:
-Cold-loop, low-pressure exhaust gas recirculation (EGR). Renault is the first manufacturer to introduce this technology in Europe.
-Thermal management technology.
-Variable displacement oil pump.
-Variable swirl technology.
-A multi-injection system designed to optimise particulate filter regeneration.
-Chain-driven camshafts.
-Maintenance-free particulate filter.
The new engine is built for Renault-Nissan at Renault’s Cléon plant, which specialises in the production of diesel engines. We rate the Company’s diesels as currently among the best on the market. Thanks to these engines, and Renault-Nissan’s precocious electric vehicle range, the Alliance expects to reduce its range CO2 yield from 135g/km today to less than 120g/km by 2013 and to under 100g/km by 2016.
As you would expect, a stop-start system is fitted.
Purely in terms of volumetric efficiency — not particularly meaningful in itself, of course — the R9M is very impressive, offering 130 HP and 320 NM from 1598 cm3. This compares with the best the opposition can offer thus:
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As we can see, the R9M manages a remarkably good fuel return when powering the very heavy Scénic. (The Octavia, like most cars with Volkswagen’s TDI 105 engine, is hampered by its wide-ratio five-speed gearbox.)
Its combined-cycle fuel consumption over the NEDC is 20 per cent. better than the 1.9 dCi 130 engine it replaces, while CO2 emissions have been cut by 30g/km.
The design process for the new engine began in 2006. It is a clean-sheet design, allowing the incorporation of some new technologies from the outset — notably a more sophisticated form of thermal management than was used on previous engines, an oil pump of variable capacity, and variable intake swirl. Renault claims that 75 per cent. of the engine’s 264 components are new, while most of the other 25 per cent. come from the 2 L M9R engine.
The Energy dCi 130 is the fruit of collaboration between engineers working at Reuil and Viry-Chatillon. Thanks to the privileged ties they enjoy with Renault Sport F1, the Reuil group was able to profit from the expertise of Viry-Chatillon to carry over a certain number of technologies developed by their F1 colleagues. This technology transfer was facilitated by Philippe Coblence, the design office manager for the R9M project. Coblence formerly held the same position at Viry-Chatillon where he worked on Formula 1 engines at the beginning of the 2000s.
There are three areas where F1 thinking was applied to the new Renault Energy dCi 130 engine.
First, the Energy dCi 130 engine uses a ‘square’ architecture — the bore and stroke are similar. This allows large-diameter valves to be used; all other things being equal, this favours top-end performance.
Transverse coolant flow is another significant design feature. This is common in Formula 1, and has been combined here with a double water-jacket design for the cylinder head. In F1, transverse coolant flow is used to maximise cooling efficiency and minimise downforce losses; generally, it enables a smaller and therefore less energy-consuming coolant pump to be fitted.
The double coolant jacket allows a more controlled rate of coolant flow, which is significant around the ‘hot zones’ — the combustion chambers and injector nozzles. This degree of control over cooling allows the engine to perate reliably at higher specific outputs. Coolant is taken downstream of the pump and does not flow around the combustion chambers. All cylinders are cooled identically, and system pressure is lower than with a more traditional set-up.
Work on internal friction included ‘super-finishing’ and special surface treatments. Uflex oil control rings, which have been used in F1 for more than 10 years, were incorporated from the beginning of the project. The U-shaped geometry of these rings is highly flexible and enables the ring to adapt to bore distortion — under the effects temperature and pressure — to achieve the best compromise between efficiency — scraping of oil on the cylinder liner to reduce consumption — and friction.
Philippe Coblence: ‘The principle is comparable with that of a multi-blade razor. It adapts naturally to the contour without having to exert high pressure on the cylinder wall. The result is maximum efficiency and less friction.’
Cold-running friction was tackled by reducing warm-up time using a new heat management system. This is described below. Hot-running friction was addressed principally by using a relatively short stroke — square rather than undersquare. The calibration of the piston rings and the surface treatment of the bearings — smooth thanks to high-precision machining: three passes instead of two — also contributed.
Reducing the necessary flow and pressure of coolant and oil also has an effect on internal friction. The double water-jacket and transverse-flow cylinder head cooling offer a cooling circuit with no elbows: the flow of coolant is practically natural, making it possible to use a smaller pump.
Key technologies
Downsizing requires that the performance of the previous, larger power-unit is maintained while fuel consumption improves. The fact of downsizing should also allow substantial weight-savings.
The most important technologies that Renault used to achieve these aims were:
Gas-flow dynamics: work on the acoustics of the air intake ducts to achieve the best filling of the combustion chambers. Additionally, variable swirl technology optimises filling of the combustion chambers — offering a high maximum gas-flow capacity — while minimising emissions at all loads and engine speeds by increasing intake swirl at low engine speeds.
Turbocharger technology: the low-inertia variable-geometry turbocharger provides short response times from low crankshaft speeds. The design and choice of materials both contribute.
A low compression ratio of 15.4:1 is combined with a higher maximum boost pressure than previously: 2.7 bar, an increase of 12 per cent. over the previous 1.9 engine. Reducing the compression ratio reduces pumping losses, but in isolation would reduce efficiency, which depends on the pressure difference between the top and bottom of the power stroke. Increasing the turbocharger’s maximum boost pressure makes up for this. The multiple injection pulses include one pulse timed late to assist in the regeneration of the particulate filter.
The design of the large combustion chamber bowl permits the use of seven-hole injectors for greater combustion efficiency. More, smaller holes gives higher pressure at each hole. On the other hand, injection pressure has actually been reduced — to 1600 bar (160MPa), compared with 1800 bar previously. This is counterintuitive, but the rationale was weight-saving.
Two significant technologies — low-pressure EGR and the braking energy recovery system — were introduced in the course of the engine’s development as the technologies themselves were signed off by Renault’s R&D teams. More about low-pressure (cold-loop) EGR anon. Because of the ‘feeding-in’ of technologies developed elsewhere in the Renault empire, CO2 the target for the new engine dropped from 140g/km in 2006 to 130g/km in 2007, and then to 120g/km in 2009.
Renault estimates the CO2 savings from the new engine’s various technical innovations — compared with the 1.9 dCi F9Q engine — as follows:
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Renault has a specific NVH department tasked with refinement matters, set up in 2005 and based at the Company’s Technical Centre in Lardy, France. The department employs a team of around 60. Renault describes refining an engine’s acoustic fingerprint as ‘tuning’, in the musical sense. The priority with the R9M was to cut noise as much as possible at source, reducing the need for clever mounting or excessive sound-proofing.
Acoustics specialist Gilles Nghiem: ‘The range of acoustic tests we carried out on the Energy dCi 130 engine enabled us to guarantee vibratory reliability and minimise noise generation without having to resort to encapsulation, since noise was dealt with at source. Scénic’s acoustic performance with this powerplant is worthy of a D-segment vehicle, while exterior noise does not exceed 72 decibels, a threshold championed by the Golden Decibel.’
The R9M is the first engine to have enjoyed the NVH department’s expertise from the outset of its development. The department’s work on the engine involved fine-tuning the pitch of generated noise, as well as reducing its quantity, and acoustic engineers also worked on ‘vibratory reliability’ issues.
Renault’s Energy dCi 130 engine is the fourth diesel engine to be developed within the framework of the Renault-Nissan Alliance, following the 2.0 dCi (M9R), 3.0 dCi (V9X) and 2.3 dCi (M9T) powerplants. The R9M project is of key importance for the Alliance, since it represents large volumes in Europe for both brands: as well as the Mégane range, the power-plant will be used by Nissan in assorted C-segment models. Nissan’s input into the project was in the area of production engineering.
In detail
Downsizing was achieved by reducing piston stroke and the size of the moving parts: crankpin and con. rod. The swept volume of the cylinder has been reduced by 16 per cent.
Performance has been maintained thanks to a higher turbo boost pressure. This approach has enabled the combustion chamber’s swept volume to be reduced with the same number of cylinders.
When running exclusively in built-up areas, fuel savings as a result of the stop-start system can exceed a litre per 100km. The system comprises a controller, which instructs the ECU to cut the engine when three conditions are met: the transmission is in neutral, the clutch pedal is released, and the car’s speed is ‘close to zero’ (our inverted commas). 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. To cope with the engine’s repeated starting, the specification of the starter motor has been uprated, as have the starter ring gear, and the fuel injection system — the pump and injectors. The engine has been engineered for 410,000 starting cycles — the equivalent of intensive use over more than 300,000km), which is almost seven times more than the same figure for a conventional engine. Renault set out to develop a system that motorists will not even be aware of; restarting requires only a brief touch on the clutch pedal.
For safety, two additional functions have been built into the system. When the vehicle is facing downhill, the engine automatically restarts when the driver lifts off the brake pedal; and the engine automatically restarts if it stalls.
The regenerative braking function (kinetic energy capturing) offers an estimated CO2 saving of three per cent. by charging the battery on overrun and under braking, but not when the engine is under load. Functions which consume electricity are directly fed by the battery to isolate the alternator from fluctuating loads.
Low-pressure (cold-loop) EGR also saves around three per cent. in CO2. EGR cuts emissions by recycling exhaust gases and re-introducing them into the combustion chambers to reduce combustion temperatures and minimise the production of nitrogen oxides. With a conventional (high pressure) EGR, exhaust gases are recovered as they exit the combustion chamber and are still very hot as they are re-introduced into the air intake. Although this functions to minimise the production of nitrogen oxides during combustion, it raises the intake air temperature: this restricts the amount of oxygen available for combustion, because hot air is less dense than cold air.
For the R9M, Renault is using low pressure EGR, which recovers exhaust gases further downstream, after they have passed through the turbocharger and particulate filter. They are cooled in a low pressure intercooler before being mixed with intake air. The mixture of intake gases is then cooled by air in the turbocharger intercooler 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 intake 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 compared with a conventional EGR.
Low pressure EGR technology calls for an engine architecture that minimises 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 thus more efficiently, as well as the fitment of a compact and efficient low pressure EGR circuit.
Thermal management speeds up the rate at which an engine reaches its working temperature. The efficiency of a cold-running engine — below 80°C — is hampered in two ways.
When the combustion chamber is cold, the combustion process is poor and incomplete, and produces a high quantity of hydrocarbons and carbon monoxide. Fuel consumption also suffers. And 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. (Note that it is possible but extremely costly to produce a synthetic multigrade lubricant with a viscosity index of 1 — in other words, an oil that doesn’t change its viscosity over the temperature range within which lubricants are tested.)
The thermal management system uses a solenoid valve located in the cooling circuit upstream of the cylinder head and block. When the engine starts from cold, the valve is closed, preventing coolant from circulating around the combustion chambers. This causes the cylinders to reach their working temperature more quickly. Because the oil is in contact with the cylinders, it, too, warms up more quickly. During this phase, no water flows between the engine and the exterior cooling system. However, to cool the low-pressure EGR loop and to provide cabin heating, it is necessary for water to flow around the engine.
The thermal management system does not replace the thermostat, which controls the engine’s temperature by controlling water flow through the radiator. The thermal management system and the thermostat are two systems which function together: the former operates during the warm-up phase, while the latter controls the temperature once the engine is warm. The thermostat opens at 85°C.
With a variable displacement oil-pump, the capacity of the pump is adjusted as a function of the engine’s needs — a function of engine speed — to minimise the energy needed to drive the pump. The capacity of a conventional oil pump is fixed, with oil pressure capped by a relief valve; pumping the oil the engine doesn’t need through the relief valve obviously wastes energy. Variable flow pumps do away with the need for a relief valve.
Variable swirl technology is estimated to give a CO2 saving of around 0.5 per cent. The term ‘swirl’ refers to the rotation of intake air about a vertical axis inside the cylinder, much like a cyclone. The swirl is produced during the induction phase and is amplified by the upward movement of the piston. Swirl is very useful for efficient combustion, but conventionally it depends on crankshaft speed: the faster the speed at which intake air enters the cylinder, the more swirl. This is intuitive. So at low engine speeds, swirl is relatively limited. At least, this is the case if the shape of the intake tracts and ports is fixed; of course, in the past the path of the intake air certainly was fixed.
But if we can find a way of varying the path of the intake air as a function of engine speed, then swirl can be maintained at low engine speeds.
In the R9M engine, Renault controls the amount of swirl by means of a flap 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, increasing turbulence. The mixing of air and fuel is at its most energetic, producing efficient combustion. However, as crankshaft speeds rise, pumping losses increase, restricting airflow; so the swirl flap can be opened, allowing a greater maximum airflow capacity. This allows greater top-end power, while the higher engine speed maintains swirl.
Note that the term ‘squish’ refers to the tumbling action of intake air forced from the piston crown into the piston-bowl as the piston moves upwards.
Members of the American Chemical Society can read this paper: Kibum Kim, Jaewoo Chung, Kihyung Lee and Kwansoo Lee: Investigation of the Swirl Effect on Diffusion Flame in a Direct-Injection Diesel Engine Using Image Processing Technology; Energy Fuels, 2008, 22 (6), pp 3687-3694; DOI: 10.1021/ef8003224; 20 October, 2008. :More.
A multi-injection strategy is universally used with modern diesels. It means simply that the injector fires more than one injection pulse into the engine. This is used to ‘shape’ the combustion process. In addition to this established strategy, the new Renault engine adds an extra three injection pulses, timed very late in the combustion cycle. The fuel used for the last two post-injections produces a reaction in the exhaust line, inside the catalytic converter, thanks to the increase in the exhaust temperature caused by 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 multi-injection strategy is employed to minimise the amount of the fuel used to regenerate the particulate filter and to limit dilution of fuel with the engine oil. As well as lowering CO2 emissions, it also permits extended oil change intervals.
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