Fuel injectors mix fuel and air before combustion in internal combustion engines. There are two main types: direct injection injects fuel directly into the cylinder, while indirect injection mixes fuel and air in a separate chamber first. Direct injection is more efficient but also more prone to issues. Performance can be increased by modifying injectors to have higher discharge coefficients, larger nozzle areas, and greater pressure differentials, but this also reduces fuel efficiency.

1. Fuel Injectors MAE 442 Mitch Rieck, Arie van Eyk and Brandon Kaufman 12/9/2009

2. Outline Background History Comparison to Carburetion Types Direct Injection Indirect Injection Applications Calculations Formulas Graphs Modifications High Performance Fuel Efficiency Durability Conclusions References

3. Background All internal combustion engines require a device to mix the fuel and air before being ignited by the spark plug The two types we will look at are Mechanical Direct and Mechanical Indirect injectors

4. History Fuel injectors have been around since the 1950’s Herbert Akroyd Stuart developed the first fuel injection system for a gasoline engine. Robert Bosch improved Herbert’s and adapted it for use in the diesel engine.

5. Carburetion Carburetion was replaced by the fuel injector. The last Carburetor that was installed in an American automobile was in 1990 Uses a simple throttle plate to control the volume of air flow through the pipe

6. Types After the carburetor there are two main types of fuel injection, direct and indirect. The main difference between direct and indirect injection is the layout of the injection system, the indirect injection system actually has a small swirl chamber above the cylinder, where the fuel is injected, this chamber also contains the spark plug, which is needed to start the engine, the direct injection system has the injection nozzle actually fixed to the top of the combustion chamber, usually the piston on the engine with this type of injection system has a crown shape in the top to create the needed air/fuel mixture.

7. Indirect Injection Indirect injection is used on most automobiles today. Before the fuel enters the piston cylinder it mixes with the air in a separate chamber. When the correct pressure is reached it is released into the piston cylinder for combustion.

8. Open view diagram Indirect Fuel Injector

9. Exploded view diagram Needle Valve Multiport injector Compression Bushing Valve Spring Injector Housing Nose Cover

10. Direct Injection In a direct-injection system, the air and gasoline are not pre-mixed. Air comes in through the intake manifold, while the gasoline is injected directly into the cylinder. The piston head is curved to create a swirl at high pressures in order to ensure a balanced air-fuel mixture.

11. Open view diagram Direct Fuel Injector Photograph courtesy of Mitch Rieck Spray Tip Fuel Passageway Valve Spring Air Intake

12. Advantages/Disadvantages Indirect Injection Advantages: High rate of swirl over wide range of engine speeds Does not require expensive, ultra high pressure injection system Less chance of injector blockage due to self cleaning pintle injectors Disadvantages: Poorer fuel consumption due to lower thermal efficiency Higher compression ratio required to aid starting Direct Injection Advantages: Cold starting is easier More Economical Smaller combustion space, better thermal efficiency Disadvantages: Tend to be noisy More prone to blockages due to small injector holes Lower power output Slower swirling, particularly at low engine speeds

13. Comparison Cadillac CTS: Two versions (same 3.6L V6) one direct and one indirect. Indirect produces 263 horsepower and 253 lb-ft torque Direct produces 304 hp and 274 lb-ft torque Despite the additional power, EPA fuel economy estimates for the direct injection engine are 1 MPG higher in the city (18 MPG vs 17 MPG) and equal on the highway Sidenote: Cadillac's direct injection engine runs on regular (87 octane) gasoline. Competing cars from Infiniti and Lexus, which use 300 hp V6 engines with indirect injection, require premium fuel. http://www.cadillac.com/pages/open/cts.do

14. Applications Direct Injection Compression ignition (diesel) Two stroke (exhaust port can be allowed to close before the mixture is injected, greatly reducing exhaust emissions. ) Indirect Injection Spark Ignition Wide range of four stroke engines

15. Calculations Calculations will focus around the power output which will be calculated using the relationship between horsepower and fuel mass flow rate. Trends showing the effects of each variable on the fuel flow rate will be shown in graphical form.

16. Formulae During injection, the mass flow rate of fuel through an injector is: The total power output is then calculated using:

17. Formulae (cont.)

18. Graphs Three different fuels were used, each having a different Heating Value and density: Gasoline – 43,000 kJ/kg, 702.5 kg/m^3 Light Diesel – 42,500 kJ/kg, 815 kg/m^3 Ethanol – 26,950 kJ/kg, 789 kg/m^3 The following values are common: Discharge Coefficient – 0.7-1.0 Nozzle Flow Area - 0.2-1.0 mm Pressure Differential – 20-200 Mpa

19. Graphs

20. Graphs

21. Graphs

22. Analysis The graphs tell us the higher the rate of fuel consumption the more horsepower we are producing. One can increase the discharge coefficient by increasing the number of valves, but it is very difficult to achieve a coefficient of 1.0. Power increased by ~2,000hp for the gasoline engine for a coefficient of 0.7 and 1.0.

23. Analysis (cont.) By increasing the nozzle area, more fuel is entering the chamber and creating more combustion. This increased horsepower from 4,000hp to 11,000hp in the gasoline engine. It is observed that changing the pressure differential by 180 Mpa, we increased the power by ~7,500hp.

24. Modifications – High Performance Modifications were based on the calculations shown in the graphs. Horsepower increases linearly with increasing Discharge Coefficient. Horsepower increases linearly with increasing Nozzle Flow Area. Horsepower increases logarithmically with increasing Pressure Differential.

25. Modifications – Fuel Efficiency Even though power is increased, by increasing the fuel flow rate, one would be using more gas. So, it is best to maximize performance and lower fuel consumption through fuel efficiency. Engine sensors, catalytic converters, and performance chips are all used to increase fuel efficiency.

26. Modifications - Durability The biggest obstacle in durability is clogging of the fuel injectors. It is recommended to replace fuel injectors every 25,000 miles. One can also use a fuel injector cleaner or cleaning kit to reduce clogs.

27. Conclusions Injection is superior to carburetion Indirect injection is easier and therefore more common to implement Direct injection is more efficient Increasing the pressure differential across a fuel injector is the most effective way to improve performance Increasing the nozzle area is the easiest

28. References http:// www.howcarswork.co.uk/modules/articles/article.php?id =7 http://auto.howstuffworks.com/question3771.htm http:// en.wikipedia.org/wiki/Fuel_injection http://www.chathamfuel.on.ca/ http://ezinearticles.com/?Fuel-Injectors:-Time-To-Replace?&id =63453 Pulkrabek, Willard W. Prentice Hall 2004. 2 nd Edition. “Engineering Fundamentals of the Internal Combustion Engine”. pp. 199-240