5 August, Tokyo Mitsubishi Motors Corporation announces the development of the new 4M41 3.2-liter in-line 4 cylinder DI Diesel.

Derived from Mitsubishi's current 4M40 2.8-liter indirect injection diesel, the new 4M41 DI^*1 diesel engine features a larger displacement, together with a fuel injection system that injects fuel directly into a combustion bowl on the top of the piston. The conversion to direct injection reduces the heat losses normal in an indirect injection diesel where fuel is ignited in a combustion chamber in the cylinder head. This, together with the improved breathing efficiency stemming from the new 4-valve DOHC configuration, realizes about 25%^*2 improvement in fuel consumption, and about 25% increase in power output.

These innovations enable the 4M41 3.2-liter in-line DI diesel engine to meet the requirements of Japan's Long-term Emissions and Year 2005 Diesel Vehicle Fuel Consumption regulations. The new engine will power a new-design PAJERO model due to be launched in September.

4M41 DI Diesel Engine

Outline introduction

1. Development aims

• To achieve class-topping^*3 levels of performance, fuel efficiency and quietness.

2. Principal features

• The current 4M40 engine has been given a wider bore and longer stroke to enlarge the displacement capacity, and a new DOHC valvetrain operating 4 valves per cylinder.
• The cylinder head locates two intake and two exhaust valves for each of the four cylinders, and uses high-efficiency cross-flow intake and exhaust ports.
• The injector nozzles are located centrally above each cylinder, thereby promoting a more even distribution of spray mist in the combustion chamber set in the top of the piston.
• The use of an electronically controlled high-pressure fuel injection pump raises injection pressure from the current 40MPa(400kgf/cm²) to 120 MPa(1,200kgf/cm²). This achieves greater atomization of the injection spray, thereby promoting a better mixture of air and fuel and realizing cleaner emissions and better fuel consumption.
• The use of an EGR cooler and a oxidation catalyst promotes cleaner emissions. Cooling the re-circulated exhaust gases effects a significant reduction in NOx, and limits increases in black smoke. The oxidation catalyst effectively reduces particulate matter.
• Engine noise levels have been reduced with the use of a larger engine cover, and the use of a back-lash eliminator for the injection pump gearing. The use of two-spring injection nozzles reduces combustion noise at idling.

Specifications: 4M41 DI vs 4M40

		4M41 DI	4M40
Bore x stroke (mm)		98.5 x 105.0	95.0 x 100.0
Displacement (cc)		3,200	2,835
No. cylinders		In-line 4
Valve train	Type	DOHC	SOHC
	No. valves	2 intake, 2 exhaust	1 intake, 1 exhaust
Compression ratio		17 : 1	21 : 1
Combustion mode		Direct injection	Swirl chamber

3. Benefits achieved

(1) Power output characteristics

• The injection of fuel directly into the cylinder, the larger displacement and the 4-valve DOHC valvetrain realize increases of about 25% in power output and about 20% in torque over the current engine.

(2) Fuel consumption

• As the following chart shows, the new 4M41 DI engine returns about 25% better fuel consumption than the current model.