Vehicle Engines - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 140

Table 9.8 Main operation parameters in the self-ignition engine
Operation modes Physical properties

Mixture formation The compression in self ignition engines is from 16:1 to 24:1, and in spark ignition engines from 7:1 to 13:1. Diesel fuel does not

produce knocking, so the engine can ignite the air and fuel mixture at high pressures and high combustion chamber temperatures.
The combustion air is compressed to (30-35) 9 10 5 Pa (435-508 psi, i.e., 62.657-73.099 lbf ft -2 ) in naturally aspirating engines
and to (80-110) 9 10 5 Pa (1,160-1,595 psi, i.e., 1.67-2.30 9 10 5 lbf ft -2 ) in charged engines [ 45 ]
The compression of the engine has a decisive effect on the cold start characteristics, the torque, the fuel consumption, and the
noise and pollutant emissions. The temperature of up to 700-900C (1,292-1,652F) is sufficient to ignite the fuel which is
injected into the combustion chamber [ 46 ]

Valve propulsion Valves are moved by the camshaft. Conventional camshafts are made of steel and used to regulate the valves [ 47 ]. Valves are usually

made from two metals and a central, perpendicular arrangement of the injection nozzle. A four valve system has two inlet and
two exhaust valves which produce optimal gas exchange and cylinder filling. In the near future, the mechanical camshaft
regulation of the valves could be replaced with electronic regulation. However, in the distant future, variable valve regulation in
combination with Common Rail systems will make the camshaft redundant

Preheating of fuel and
air

Preheating the fuel and air is important for reducing exhaust gas emissions, especially during cold starts. In very cold weather,
additional burners are necessary [ 48 ]

Current Common Rail injection pumps use pressures above 1,000 9 10 5 Pa (14,505 psi, i.e., 20.89 9 10 5 lbf ft -2 ). Specific
applications that must be protected against high temperatures in the combustion system should use a lower pressure than in the
past by approximately 800 9 10 5 Pa (11,604 psi, i.e., 16.71 9 10 5 lbf ft -2 ). However, tendencies show in the direction of higher
pressures and lower drop diameters. Radial piston pumps should be used for higher efficiency, longer life span, lower weight, and
reduced noise [ 49 ]

Common Rail

Sealing system Cylinder head sealing must be adapted to the increasing pressures [ 50 ]. The materials of the cylinder head define their use, which

greatly influences the life span of the engine. Wave can be sealed with radial sealing. Crankshaft seals have to cope with high
pressures and temperatures

Cooling system The temperature of the self ignition engine is regulated by two different cooling systems [ 51 ]. Wet cylinder barrels and bored or

calibrated ducts are used for interior engine cooling. Engine temperature is regulated by ambient air. Today, cooling fans with a
special coupling are used which turn on in response to the engine temperature. The precise regulation is important because large
fans in modern heavy commercial motor vehicles use a high proportion of the engine power, between 15 and 21 kW (20 and 28
HP). Future engines will work with higher combustion temperatures and therefore they must be intensively cooled

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