BMW M21

M21
Overview
Manufacturer BMW
Production 19831991
Combustion chamber
Configuration Inline-6
Displacement 2443 cm³
Cylinder bore 80 mm
Piston stroke 81 mm
Cylinder block alloy Cast iron
Valvetrain OHC
Compression ratio 22:1
Combustion
Turbocharger Garret (85 kW engines only)
Fuel system Swirl chamber injection
Fuel type Diesel fuel
Cooling system Water-cooled
Output
Power output 63 – 85 kW
Torque output 152 – 220 Nm
Chronology
Predecessor None
Successor M51

The BMW M21 is a six-cylinder-inline-diesel engine developed by the bavarian engine manufacturer BMW. The engine with swirl chamber injection is based on the otto engine M20[1] and was produced for BMW by the upper Austrian Steyr engine plant from 1983 to 1991. It was succeeded by the M51.[2]

Background

In the 1970s BMW decided to develop an engine, which would both be powerful and have a good fuel economy. This was caused by the oil crisis in 1973. In 1975 a group of BMW engineers started working on the M21 diesel engine, the otto engine M20 was taken as the basis. In 1983 at the IAA, the first passenger car was shown to the public which made use of the 85 kW M21. It was the E28 524td, which has a top speed of 180 km/h and reaches 100 km/h in 12,9 s. This 5er-BMW was the fastest series production diesel car in the world back in 1983. It has a fuel economy of 7,1 l /100 km.[2]

Technical description

The M21 is a water-cooled[3] six-cylinder-inline-diesel-engine with a cast iron block and OHC valvetrain. The camshaft is driven by a belt,[2] each cylinder has one inlet and one outlet valve.[1] Compared to the otto engine M20, the M21 has reinforced connecting-rods, cylinder heads, pistons, valves[2] and a reinforced crankshaft[1] with seven[3] bearings. For faster engine startup the M21 has a glowplug system called instant start, which reduces the time to reach starting temperature compared to similar diesel engines.[2] The fuel is injected into swirl chambers.[1] The mechanical injection was replaced in 1987 by an electronic diesel control system in the turbocharged engine.[4] The electronic diesel control results in better torque.[1] A Garret turbocharger[5] is used in the 85 kW engine, it lacks an intercooler. The engine with the EDC has a smaller turbocharger, which responds quicker.[1] Starting in 1985, BMW offered the M21 as a naturally aspirated engine, which was popular in countries with a high motor vehicle tax.[2]

Models
EngineBore × StrokeDisplacementCompressionRated PowerMax. TorqueRedlineYear
M21D24[3]80 × 81 mm2443 cm³ (149 in³)22:185 kW (114 hp) at 4800 min1210 N·m (155 lb·ft) at 2400 min15350 min11983
220 N·m (162 lb·ft) at 2400 min15350 min11987
63 kW (84 hp) at 4600 min1152 N·m (112 lb·ft) at 2500 min15150 min11985

Applications:

See also

References

  1. 1 2 3 4 5 6 Andreas in Bimmer: Die BMW-Sportdiesel: Von 524td E28 über 530d E39 bis BMW M550d F10, published at the 21st of January 2012, retrieved at the 9th of April 2015. (german)
  2. 1 2 3 4 5 6 Ronan Glon in RanWhenParked.net: 30 years ago: BMW introduces its first diesel engine, published at the 22nd of Juli 2013, retrieved at the 9th of April 2015.
  3. 1 2 3 Meyer Motoren: BMW M21. Retrieved at the 9th of May 2016. (german)
  4. 1 2 3 4 BMW M21 engine page. Retrieved at the 9th of May 2016.
  5. Auto Motor und Sport: Der zweite 5er von BMW: Die Baureihe E28 Der unscheinbare Revoluzzer, retrieved at the 9th of April 2015. (german)

External links

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