Fuel Standards

In order to provide fuel with suitable properties for use in a diesel engine and limited variability work began in the 1990s in Germany to define a fuel standard for rapeseed oil fuel. This work has culminated in the establishment of a DIN standard for rapeseed oil fuel

Accompanying research for the standardisation of rapeseed oil as fuel for vegetable oil suited diesel engines in vehicles and combined heat and power plants - German document examining work towards a fuel standard.

• Acid Value

Oil Production

Vegetable oils are commonly extracted from oil bearing plants by crushing or pressing oil rich nuts and seeds.

• Solvent extraction - on a large commercial scale oil seeds are crushed and then mixed with a solvent to strip as much oil from the solid matter. The solvent is then recovered leaving the oil and seed cake.
• Cold pressing - on a smaller scale oil is extracted by simply pressing the seed. Oil yields are not as high as with solvent extraction. The process is simpler and more suitable for decentralised production.

Used cooking oils

Often used cooking oils and fats are cleaned and utilised as diesel engine fuel.

Injection pressure

Increased injection pressure has been shown to improve the otherwise degraded performance of fuel injectors when spraying vegetable oil. This is not as significant in indirect injection engines where the fuel is further atomised in the pre chamber before being drawn into the engine cylinder.

Papers examining effects of injection pressure with vegetable oils-

Injection Characteristics of an In-line Fuel Injection System Using the Alternative Fuels

Study on rapeseed oil as alternative fuel for a single-cylinder diesel engine

EFFECT OF FUEL TEMPERATURE AND AMBIENT PRESSURE ON A COMMON RAIL RAPESEED OIL SPRAY

Stationary Applications of Liquid Biofuels

Influences of Alternative Fuels GTL, RME & ROR on Combustion and Emissions of a Modern HD-Diesel Engine

Phase Doppler anemometry measurements of a dense rapeseed oil spray

The analysis of spray parameters of fuels of different viscosity sprayed by a typical and rotary-swinging needle injectors

Study on noise of rapeseed oil blends in a single-cylinder diesel engine

Factorial analysis of diesel engine performance using different types of biofuels

Study on cottonseed oil as a partial substitute for diesel oil in fuel for single-cylinder diesel engine

Injector opening pressure

Where applicable increasing the injector opening pressure provides a higher injection pressure at injector opening and a higher peak injection pressure. Injection timing will become more retarded due to the extra time required for the pump to reach the higher opening pressure. The injection rate, duration and quantity of fuel injected is also likely to be effected.

Some more modern engines such as the Volkswagen group Tdi engine with VP 37 injection pump and the BMW M51 use two stage injectors with opening pressures set for each stage, pilot and main and a needle lift sensor that monitors the timing of start of injection so that the ECU can maintain the correct start of injection. Special equipment is required to set the main stage opening pressure and there are a limited number of injection specialists able to complete this work. Modifying only the pilot opening pressure will in effect advance the main injection event due to the ECU correction.

Combustion after cold starting

Engines will not burn fuel as efficiently until the whole block is heat soaked which can take some time (20 mins+?). Operating strategies can be altered or devices added to improve combustion during this period:

• combustion chamber glow plugs that are kept energised after cold starting
• inlet air heaters
• cold running timing advance modules such as KSB modules fitted to Bosch VE injection pumps
• increasing the cold engine idle speed
• pre heating the engine block / coolant
• the use of an exhaust brake

Combustion during periods of low engine load

Rostock presentation

Due to their differing chemical composition plant oils behave differently to conventional diesel fuel in a diesel engine. The University of Rostock presentation - Rapeseed as an Agricultural Fuel shows results from tests of rapeseed oil and diesel fuel performed as part of a Tractor fleet project

• page 5 - Fuel standards for diesel, biodiesel and rapeseed oil.
• page 6 - Surface tension of diesel, rapeseed methyl ester and rapeseed oil at different temperatures.
• page 7 - Injection pressure and volume of diesel and rapeseed oil at 90° Celsius and different injector pump speeds.
• page 8 - Relative difference of fuel spray drop diameter at different distances from the injector nozzle.
• page 9 - Beginning of injection at different engine loads - with rapeseed oil the beginning of injection is 1 degree advanced.
• page 10 - The burn rate of diesel, rapeseed oil and adapted rapeseed oil at different degrees of crank rotation - the burn rate of rapeseed oil peaks 9 degrees of crankshaft rotation later than that of diesel.