Port Fuel Injection VS. Direct Fuel Injection

The Basics of DFI

The main focus of DFI is to effectively and precisely control the fuel-to-air ratio. To achieve a level of precision beyond port fuel injection, DFI injects fuel and air separately into the combustion chamber, rather than a mixture of the two. When fuel is added to the combustion chamber without air, it can be much more precisely measured and evenly spread throughout the volume of the cylinder. This makes a higher and more desirable fuel-to-air ratio possible. Starting in the fuel tank, gasoline is removed from the tank by means of a low-pressure fuel pump that rests inside the tank. As the fuel approaches the engine, it is passed through a high pressure fuel pump. This pump, which runs at significantly higher pressures than the low pressure pump (4-13 MPa vs .35 MPa) forces the gasoline into a looped fuel line. The high pressure pump is capable of varying the pressure in the fuel line, accounting for changes in power demands of the user and changes in atmospheric pressure without loss of performance. In the loop, fuel is sent to the individual injectors located above each combustion chamber. Each injector is controlled separately by the car’s computer, or Engine Control Unit (ECU). The ECU itself receives input from multiple sources, such as the pressure sensors and fuel pumps, and controls all of the mechanical aspects of the system, such as the adjustment of fuel pressure and the timing of the engine’s components.

APPLICATION OF DIRECT FUEL INJECTION TO INCREASE SUSTAINABILITY OF GASOLINE INTERNAL COMBUSTION ENGINES

Matthew Dainton and Jonathan Mozelewski

Overview of Direct Fuel Injection Technology

Due to the increased demand for higher efficiency in gasoline internal combustion engines, automobile manufacturers are forced to search for effective strategies that are new or not as commonly used to maximize gasoline energy. While many manufacturers are relying on turbocharging and cylinder deactivation to accomplish their goals, direct fuel injection (DFI) remains relatively untapped. DFI is a mechanical system of fuel delivery that provides vast improvements in both power and efficiency over current fuel delivery methods (Port Fuel Injection or PFI). By providing an immediate supply of pure fuel, unmixed with oxygen to the combustion chamber, DFI changes how fuel is mixed. This change is more efficient than PFI’s method of mixing fuel and air, as it creates a higher compression ratio (ratio of air to fuel), which is more desirable for combustion efficiency and power. In this paper, the authors will discuss the basics of an internal combustion engine, the current method of fuel injection (PFI,) and introduce multiple aspects of the technology of DFI. The paper will also consider the benefits DFI can provide to automakers, ethical concerns associated with DFI, and DFI as a sustainable technology leading into the future.

Basics of an Internal Combustion EngineDirect fuel injection (DFI) affects how fuel is delivered to the combustion chamber of the engine, ultimately affecting how combustion occurs. In order to realize the impact of this system on a gasoline engine, it is important to understand how a gasoline engine works, and the role that fuel injection has in it. An engine requires three basic components to cause an explosion in the combustion chamber: air, fuel, and a spark. The engine encounters all of these elements in a repeated cycle, as diagramed step-by-step in the figure.

1. Air first fills the chamber in an intake “stroke”, one full movement of the cylinder to the bottom or to the top of the combustion chamber.

2. In the compression stroke, the cylinder ascends back to the top of the chamber, causing the volume of the chamber to decrease and the gases to compress.

3. In the power stroke, a spark ignites the compressed fuel mixture, causing the cylinder to be driven downward from the force’s explosion.

4. The spent gases are removed from the combustion chamber in the exhaust stroke, allowing the chamber to take in fresh air when the cycle repeats itself.

Measurable Benefits of DFI

Although consumers prefer to see increases in fuel economy, they do not want to see a decrease in performance as a result. When DFI is applied to an engine, the power output of that engine actually increases over that of a similar engine with PFI. As shown in the table below, power of an engine with PFI was surpassed by that of an engine that was slightly smaller, but equipped with DFI.

Chart illustrating the differences in power, efficiency, torque, and emissions between commercially available engines with DFI and PFI.

• The smaller engine with DFI (1.4 L) actually produced higher levels of power and torque than the larger engine (1.6 L) did.

• The direct injected engine was also more efficient than the larger engine, burning less fuel to go the same distance.

• The smaller engine produced its maximum torque, as well as its maximum power, in a range of engine speeds (i.e. revolutions per minute) lower than those of the larger engine.

Engine Type

Swept Volume

(L)

Max. Power (kW

at rpm)

Max. Torque (Nm at rpm)

Fuel Economy (Urban Driving) L/100km

Fuel Economy (Highway Driving) L/100km

CO2 Emission

g/km

Gasoline Engine (PFI)

1.675

5600 148

380010,5 6,0 179

TSI Gasoline Engine (DFI)

1.490

5000 - 5500

200 1500-4000

8,6 5,5 157

Sustainability

• Although costs for DFI are currently higher than those for PFI, DFI will drop in production price with time and increased use.

• DFI can be applied to more than just gasoline engines and could be combined with additional fuel-saving technologies such as turbochargers and cylinder deactivation for additional benefits.

• The principles of direct fuel injection can also be applied to alternative fuels, meaning that DFI will be relevant even when gasoline fuel becomes obsolete.

• A DFI system can be incorporated into an existing engine, saving companies time and money when compared to designing an entirely new engine.

With a wide range of applications, DFI can improve not only the efficiency of automobiles, but also the efficiency of a great number of other internal combustion vehicles. With time, direct fuel injection will prove itself as a step towards future automobiles with fuel economy that reaches the rising efficiency demands of consumers.

Port Fuel Injection (PFI)

• A common design, PFI is well-integrated into the automotive industry.

• Much cheaper than DFI because it utilizes parts that are more easily accessible than with DFI.

• Injects fuel before the air reaches the combustion

chamber.

• Operates at the outside atmospheric pressure of the vehicle.

Direct Fuel Injection (DFI)

• Beginning to become common in commercial gasoline engines

• Utilizes higher quality components than PFI, so it is more expensive

• Injects fuel directly into the combustion chamber, separately from air

• Pressurized system that runs at much higher pressures than PFI

Advantages of PFI Disadvantages of PFI Advantages of DFI Disadvantages of DFI

• Low-priced• Commonly used in modern

automobiles• Relatively simple design

• Limited air-to-fuel ratios• Loss of fuel at lower speeds

due to vaporization of fuel• Affected by outside

atmosphere pressure changes

• High control over air-to-fuel ratios

• Unaffected by changes in outside pressure

• Lowers fuel consumption• Can be added to pre-existing

engines

• More expensive than PFI to build

• More complex design than PFI

• Can release carbon emissions higher than PFI if not properly designed