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Advanced Fuel Delivery Systems


10/25/2006
By Dan Maslic

 

There are many ways to get fuel into a combustion chamber and it seems that today auto manufacturers are using every possible method. As if that were not enough, manufacturers are hedging their sales bets by developing vehicles that use many different types of fuel, and in some cases, vehicles that can burn more than one type of fuel. Common fuels used are gasoline and diesel, but now ethanol is becoming prominent as well. Not far on the horizon are home-filled natural gas powered vehicles, such as the Honda Civic (already for sale), and hydrogen powered vehicles such as BMW’s 2008 Hydrogen 7-Series. And let’s not forget that diesel is changing in 2007 to the newly mandated low-sulphur formula. To deliver these fuels to the combustion chamber, we use “Return” and “Returnless” fuel systems, Port or Direct Injection, and in some cases, a dual-mode Port and Direct Injection system. There’s so much new technology with fuel systems it’s enough to make anyone light-headed.

A ONE-WAY TICKET TO THE COMBUSTION CHAMBER

Over the years, most gasoline fuel injection systems utilized a vacuum — operated mechanical fuel pressure regulator in a “Return” style fuel system. You probably recognize the vacuum operated pressure regulator as you may have sold hundreds of them over the years due to leaks and other potential failures. In a Return-type fuel system, the fuel pump forces fuel through a fuel filter and onto the fuel rail where the fuel may be injected. When fuel rail pressure exceeds a calibrated value (through the pressure regulator’s vacuum-referenced spring/diaphragm assembly) the pressure regulator may return a portion of the fuel back to the fuel tank to maintain proper fuel pressure. Due to design tolerances and the mechanical nature of the system, return-style fuel systems are not precise in function and they allow heat transfer to the fuel tank by way of the returning fuel. This puts higher demands on the canister and vapor-recovery system. Also, since the system is based on a mechanical vacuum-referenced pressure regulator, it is by nature a passive system and not easily compensated for by the engine management computer (ECM) when trying to keep emissions in check, nor is it directly monitored by the vehicle’s On-Board Diagnostic system. To correct these issues, many gasoline-powered vehicles now have a “Returnless” fuel system. In a Returnless fuel system, a fuel rail pressure sensor replaces the fuel pressure regulator, and the ECM controls the fuel pump either directly or indirectly through a fuel pump driver module. Fuel pressure is varied by the amount of voltage applied to the fuel pump as commanded by the ECM. This has the benefits of active fuel pressure control, full compatibility with On-Board Diagnostics, and no heat transfer to the fuel tank as the pumped fuel has a one-way ticket to the combustion chamber. Since the system is actively monitored by the OBD system, faults with Returnless systems rarely go undetected. One thing to watch for is warranty fuel pump driver modules. In many performance applications, the vehicle owner may have fitted an aftermarket high-flow fuel pump to the vehicle in place of the OE pump that isn’t compatible with the fuel pump driver module. If a fuel pump driver module comes back under warranty, double check with the customer to see if a non-OE style pump was installed or have the installer check the fuel pump current draw to prevent further problems or failures.

BE DIRECT!

In Port Fuel Injection systems, fuel is sprayed out of the injectors into the intake port where it is allowed to mingle with incoming air for a while before entering the combustion chamber. During slow engine speeds and at colder operating temperatures, the fuel does not have sufficient time or capability to fully atomize. This results in higher exhaust emissions. The cure is Direct Fuel Injection (DI). Many manufacturers already use this type of injection system and it will become the norm before long. DI systems place the fuel injector directly in the combustion chamber. Since the injector sprays fuel directly into the combustion chamber, DI systems must run at much higher pressures than Port Injected systems to overcome the cylinder pressures generated during the compression stroke. DI’s higher operating pressure better atomizes the fuel and also has a cooling effect when sprayed in the combustion chamber. The benefits are a cleaner burn, lower exhaust emissions, increased power, easier starting and reduced potential for detonation. At the parts counter, you may have more requests for injector cleaning solutions, more frequent seal replacements as standard service/repair procedures, and higher fuel pump sales as many vehicles equipped with DI have two fuel pumps, one low pressure and one high pressure. Some vehicles, such as the new Lexus IS350, have a dual-mode fuel injection system utilizing both Port and Direct Injection. At lower engine speeds, fuel is injected directly into the combustion chamber. At higher engine speeds and when under higher load, a secondary set of Port injectors is activated and sprays fuel into the intake ports in addition to the fuel being injected through the direct injectors. This system allows performance and emission targets to be met but comes at the cost of added complexity and increased potential for component failure.

GAS STATION OR PUB

The alcohol that we drink is ethanol. Ethanol is also the alcohol that is mixed with gasoline to give us the fuel called E85. As the name implies, E85 is 85 percent ethanol, and 15 percent gasoline. This denatured ethanol may also be referred to as “fuel-grade ethanol.” Obviously, we cannot drink fuel-grade ethanol. GM and Ford are both making a huge marketing and sales push right now with Flex-Fuel Vehicles (FFVs) that can burn straight gasoline, E85, or any combination in between. Normal fuel systems are not compatible with E85 as the metals and seals are not designed to tolerate the alcohol found in E85. This is an important point if one of your customers calls asking for parts on what turns out to be an FFV. Compared to the standard vehicle model, many parts may be different such as fuel injectors and pumps, seals, fuel lines, even fuel filters. Double-check all part numbers when dealing with FFV parts requests. GM makes it easy to recognize their new FFVs as they all come equipped with yellow colored fuel fill caps. Ford models that may be FFVs include the Ford Taurus, Crown Victoria, Mercury Sable and Grand Marquis, Lincoln Town Car, Ford Ranger, Ford Explorer, Mercury Mountaineer and F-Series trucks with GVW under 8,500 lbs. DaimlerChrysler FFVs include Ram trucks, Caravan, Voyager and Town & Country minivans, Dodge Intrepid and Stratus and Chrysler Sebring. Some Isuzu, Mazda and Nissan pick-up trucks may be FFVs, as well as Mercedes Benz C240 and C320 models. As the price of gasoline rises (as well as political tensions) you will begin to see many more FFVs on the roads of America in the near future and must keep in mind the differences between these models and their conventional counterparts to ensure that your customer is getting the right parts for the job.

THE NEW DIESELS

Diesels have been around for a while, but they have not made a big impact on the market. In total, diesel powered vehicles still account for less than 5 percent of all new vehicle sales in the U.S. This, however, is about to change. With the new low-sulphur diesel fuel coming in 2007, many manufacturers will now offer “clean diesels” to the American public. Low-sulphur diesel fuel allows much smaller injector nozzles to be used and allows the diesel fuel to burn cleaner with less particulate matter generated in the process. Advances in diesel fuel injection have been made that result in increased power and reduced noise. One example of the new diesel technology is the electronically controlled common-rail diesel injection system. This system functions somewhat similar to a direct injection gasoline system. The major difference is that with gasoline you inject the fuel during the compression cycle, while diesel gets injected when you want to generate power. Since diesel burns as it enters the cylinder, cylinder pressure rises immediately upon diesel injection. This is where the key advancements in diesel engine control have been made. The old diesel trucks that you hear clickety-clacking down the road make that noise due to the fact that the diesel fuel is injected in one steady stream to initiate combustion. The rapid cylinder pressure rise is what creates the “clacking” sound. The new electronic common rail diesel systems separate the diesel injection events into three or more separate injection events that lower the rate of cylinder pressure rise, spreading it over a greater range of crankshaft rotation. Diesel fuel burn begins with a “pilot” or pre-injection event to preheat the combustion chamber, followed by a larger “power” or main-injection event to create engine torque, and lastly an “after-treatment” or post-injection event to help burn residual particulate matter and lower exhaust emissions. Some systems may use as many as seven different injection events under certain operating conditions. These injection events may include two or three pilot injections, two or three power injections, and one or two after-treatment events. Aside from the obvious benefits of reduced exhaust emissions and better fuel economy, the electronically controlled common rail diesel system also offers higher performance, reduced noise, vibration and harshness (NVH), and also results in a much quieter engine.

At the parts counter you will find new opportunities with diesel fuel filter sales, with water separators, fuel pumps and fuel injectors, as well as diesel engine controllers and fuel injector driver modules. Since some of the common-rail diesel systems operate at over 26,000 psi (1,760 bar), these parts and their accompanying lines and seals will be in great demand as vehicles age.













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