BMW reveals new engine family

BMW continues to roll out its last generation of petrol and diesel engines before Europe's tough new EU7 emissions laws take effect at the end of this decade.

The new B48 and B58 modular four- and six-pot engines first arrived here last year when the 328i became the 330i and the 335i became the 340i, before hitting the 4 Series as part of an upgrade in June this year.

They will then filter down to upcoming upgateds for the 3 Series GT, 1 Series and 2 Series, before powering next year's all-new 5 Series, particularly the 520i and 528i in petrol form, and the 520d and 525d in diesel form.

The new modular engines will be fitted in both north-south rear-drive cars and east-west front-drives, and will wear both MINI and BMW badges.

BMW claims the engines are smoother, cleaner and will sound nicer than the current generation as it heads towards an EU-mandated fleet-average CO2 emissions target of 95g/km in 2020.

The new laws, which will arrive midway through the engine generation’s lifespan, mean a target as low as 4.1L/100km for petrol engines and just 3.6L/100km for diesels.

The Bavarian car-maker insists the new engines will slash about five per cent in CO2 emissions across the board, deliver an extra 7kW and 20Nm and will come with direct fuel-injection, variable lift for the inlet valves and double Vanos variable timing for both the inlet and exhaust valves.

BMW has integrated the exhaust manifold and the turbocharger housings into the cylinder-heads of both the three- and four-cylinder versions of the new engines, while a new cooling system is also claimed to lower emissions.

With up to 350-bar of injection pressure for the petrol engines, BMW has separated the cooling outlets for the cylinder-head and the block so the system can cater for different thermal characteristics rather than a lowest-common-denominator approach.

While BMW claims the new motors will be inherently smoother than the current engines, they will retain the current balancing shafts on the four-cylinder unit and all-new versions have been developed for the three-cylinder motor.

All of the four-cylinder diesel motors borrow from the most powerful six-cylinder BMW turbo-diesels by using two turbochargers as standard equipment.

BMW says it does this to give it a smaller, low-pressure turbo for lower boost pressures at low- to middle-engine speeds, while there’s a bigger, higher pressure unit fitted for higher revs.

The vanes on the low-pressure turbo adjust electronically via an ECU controller and it also has its own cooling system switch, so it’s clear that this is the turbo BMW expects to do most of the work.

All of the four-cylinder engines’ turbos nestle inside steel casings, while the three-pot turbos can be either in steel or alloy, depending on the power outputs.

BMW also uses a newly designed exhaust gas recirculation (EGR) set-up in both three- and four-cylinder guises to reduce NOx levels at the tailpipe, and insists it won’t rely on thermal switches to protect the system from damage.

Rival premium brand Mercedes-Benz and other volume brands like Opel have run into criticism in Europe for switching their EGR systems off when the air temperature is too cold or too hot, rendering them useless for a big chunk of the European calendar year.

To help keep NOx emissions low, all the diesel engine variants will use AdBlue urea systems injected into the exhaust gas flow and selective catalytic reduction (SCR).

The new common-rail fuel-injection system has seen the fuel-injection pressure raised to 2200-bar for the three-cylinder engines, 2500-bar for most of the four-cylinder engines and a truly astonishing 2700-bar for the strongest four, along with improvements in sensor accuracy and fuel metering.

Oddly, the design of the cylinder, which is one of the oldest and most fundamental areas of the entire car industry, has been given an overhaul, too. Now, the diesel engine’s cylinders are a little more like truncated cones, with a bigger bore at the bottom than at the top.

BMW says this is because it reduces the long-term friction that can be caused by thermal and dynamic forces the engines go through during assembly.