Originally, gasoline engines solely used carburetors to prepare the air and gas mixture. However, the relative inaccuracy of this method has led to the development of direct fuel injection, resulting in a more efficient burn and lower emissions. Below, I’m going to explain how the system works as well as its pros and cons. It is likely that a greater number of vehicles will be built with this type of engine in the future, so it’s worth to understand its operation.
How Direct Fuel Injection Works
In most gasoline-fueled cars, the engine operates on a four-stroke cycle. In a four-stroke engine, during the first step the intake valve opens and the cylinder is filled with a mixture of gas and air. Next, the valves close and the piston moves up, compressing the mixture. After that happens, ignition is triggered, sending the piston downwards in what is known as the power stroke. Lastly, the exhaust valve opens and the piston travels upward, forcing out the waste fumes.
In a carbureted vehicle, the fuel blend is mixed before entering the cylinder on the first stroke. With direct injection, the gas is sprayed into the cylinder while the air enters through the intake manifold.
There are a number of benefits to a direct-injected engine. The primary advantages involve improved fuel economy and greater power output. Each burst of gasoline is normally measured and timed by the onboard computer, translating into greater efficiency and less pollution. In addition, the ultra-fine droplets and even the dispersal created by the system has a cooling effect on the engine that increases power across the entire RPM band.
When it’s running, the computer is continuously varying between different air-gas ratios to ensure the best performance. The three modes are “full power,” “ultra lean burn,” and “stoichiometric.” During a full power burn, the mixture is richer, enabling the car to accelerate faster and prevent knock. “Ultra lean burn” pushes the ratio as high as 65: 1, providing emission reductions under low-stress situations. “Stoichometric” mode runs the engine at a 14.7: 1 mixture, the optimum combination that ensures a 100% burn, used for moderate-stress situations.
Unfortunately, direct injection systems are more expensive and complex to build, resulting in a concentration among high-performance cars and trucks. Another drawback to these systems is the component durability. The assembly must be able to handle high-pressure gasoline as well as the heat and pressure in the cylinder for extended periods of time. Furthermore, the assembly must be very accurate in order to direct the spray properly. This tight tolerance can also make the assembly unreliable, especially if the engine is routinely placed in high-stress situations or driven for long distances.
Even though prices currently remain reliably high for these systems, their improved performance and fuel efficiency is likely to spur their adoption in additional car models. Before long, carburetors will be a distant memory.