BMW's Nice 1
The new BMW 1-Series models, announced in January, had their world premiere at the Geneva auto show.
In addition to featuring a start-stop system, brake energy regeneration and electric power steering to reduce fuel consumption as standard, the new 1-Series benefits from new four-cylinder gasoline and diesel engines.
Gasoline. The new BMW 1 Series features two variants of the new generation of gasoline engines, both using second-generation High Precision Injection direct fuel injection. This technology is able to maintain lean-burn mode throughout a particularly wide range of engine speeds.
In the new BMW 120i, the 2.0-liter engine develops maximum output of 125 kW/170 hp and accelerates in just 7.7 seconds (five-door: 7.8 seconds) to 100 km/h. Fuel consumption is 6.4 litres per 100 kilometers (37 mpg US). Compared to its predecessor, the new engine reduces fuel consumption by almost 14percent on an increase in power of 15 kW or 20 hp. CO2 emissions are 152 g/km (down 16 percent).
The new BMW 118i, with an output of 105 kW/143 hp, consumes 5.9 liters per 100 kilometers (40 mpg US—an improvement of 24 percent over the older model—and CO2 emissions are 140 g/km (down 20.5 percent).
Both these engines consume less fuel than the smaller displacement, lower-powered entry engine in the 116i.
The second-generation High Precision Injection uses jet-guided combustion rather than wall-guided. To enable this, BMW engineers had to fit the piezo injectors between the valves immediately adjacent to the spark plug despite very tight space constraints in the cylinder head.
The jet-guided method enables more precise metering of fuel quantities, and ensures a considerably faster and more efficient mixture preparation without losses caused by fuel mist on the cylinder walls.
An electric pump in the fuel tank that only switches on when needed supplies the high pressure pump on the cylinder head. The high pressure pump generates a pressure of 200 bar in the supply line for the four injectors. The piezo nozzles, which open to the outside, ensure a stable, conical injection jet entering the combustion chamber. In addition, the fuel quantity used in one stroke can be injected in several portions. In this manner, a highly controlled, clean and efficient lean-burning combustion process is achieved over a broad load and engine speed range.
In lean-burn mode, also known as stratified cylinder charging, intersecting layers of the fuel-air mixture of varying compositions build up within the combustion chamber. As the distance from the spark plug increases, the proportion of gasoline in the mixture decreases. A layer of fuel/ air mixture sufficiently rich and therefore easily ignitable is formed only in the direct vicinity of the spark plug. Once this layer of fuel and air has ignited, the leaner layers at a greater distance from the spark plug will also start to burn in a smooth, clean and consistent fashion.
Among other innovations to reduce engine weight, BMW used a lightweight hydroforming camshaft and a switchable intake manifold (DISA) made of synthetic material.
The new lean-burn engine features a main catalytic converter close to the engine and downstream catalytic converters for the prevention of NOx emissions.
BMW says that it will introduce a 1.6-liter four-cylinder member of the new gasoline engine range develops 90 kW/122 hp and maximum torque of 160 Nm/118 lb-ft at some point in the future.
Diesel. The new 2.0-liter diesels feature an all-aluminium crankcase, turbocharging, third-generation common rail injection, diesel particulate filters positioned close to the engine and other innovations.
Both are of the same displacement. The variation in their outputs results from modifications to the injection and charging technologies. With maximum output of 105 kW/143 hp and maximum torque of 300 Nm/221 lb-ft, the basic configuration of the new diesel powertrain exceeds the former engine by 15 kW and 20 Nm/15 lb-ft, respectively.
The more powerful of the two new four-cylinder diesels offers 130 kW/177 hp, which is 10 kW greater output than the former version.
Its maximum torque equals 350 Nm/258 lb-ft (plus 10 Nm/7 lb-ft). The rpm range is extended by 10 percent per cent in both models.
Compared to the former versions of the engines, the new drive units are characterized by reduced weight and considerably lower fuel consumption and emission values despite significantly higher output. Fuel consumption in the new BMW 118d in the EU test cycle compared with the predecessor model is lower by 16 percent despite an increase in output of 15 kW.
The new engines weigh 17 kilograms less than the four-cylinder diesel engines of the previous generation. The largest percentage in weight reduction came with the new aluminium crankcase, which replaced the grey cast iron block in use until now.
The intake ducts of the newly constructed cylinder head are laterally positioned. To achieve the lowest possible emission values, the spiral filling duct is electronically controlled with continuously variable settings.
The large diameter valves facilitate the ready exchange of gasses and now come in a vertical arrangement. The incoming fresh air is made turbulent in the swirl channel, improving interior mixture formation.
While the basic configuration of the engine operates with an injection pressure of 1,600 bar and fuel metering is handled by magnetic valves, the diesel fuel in the larger of the two engine variants is delivered at a pressure of 1,800 bar by four piezo injectors. Because the fuel is injected in up to three portions per stroke, the flame spreads gently, primarily to the benefit of the running characteristics.
Each of the engines, which have outputs of 105 and 130 kW, respectively, is equipped with an exhaust turbocharger with variable turbine geometry. Through this technology, power development can be optimally adjusted to all load ranges. Using an electric actuator, the turbine’s control apparatus is adjusted to the specific requirements with a high degree of accuracy and minimal delay. This ensures an immediate response at low engine speeds and high power density under full load. Maximum torque is available between 1,750 and 2,500 rpm for the 105 kW motor and 1,750 and 3,000 rpm for the 130 kW variant.
The new 118d offers fuel consumption of 4.7 l/100km (50 mpg US)—19 percent better than its predecessor—and CO2 emissions of 123 g/km—a decrease of 18 percent.
This article was originally published on Green Car Congress on March 8, 2007