Which is better, combined injection or direct injection?
4 Answers
The differences between combined injection and direct injection are as follows: 1. Different engine systems. The most critical system of a direct injection engine is the high-pressure fuel injection system, which mainly consists of four parts: the engine control module (ECM), high-pressure fuel rail, high-pressure fuel pump, and fuel injector. A combined injection engine has both direct injection and manifold injection systems. 2. Different fuel injection methods. Direct injection is a technology that directly injects fuel into the cylinder to mix with the intake air, while combined injection combines the advantages of manifold injection and direct injection. Under low-load conditions, the manifold injector sprays fuel during the cylinder's intake stroke, allowing the mixture to enter the cylinder, and then the cylinder injector sprays fuel during the compression stroke to achieve stratified combustion. Under high-load conditions, only direct injection is performed during the compression stroke, thereby improving the engine's efficiency and avoiding the emission issues caused by excessive oxygen under low-load conditions in direct injection engines. 3. Different costs. Since a combined injection engine integrates both direct injection and manifold injection systems, with two sets of fuel pumps and fuel supply pipelines, its cost is significantly higher than that of a direct injection engine.
I've been driving for over a decade and have experience with both injection systems. Direct injection delivers quick power response with strong acceleration when you step on the gas, making it especially thrilling on highways. However, it tends to accumulate carbon deposits in stop-and-go city traffic—my direct injection car needed throttle body cleaning at just over 30,000 kilometers. Dual injection places injectors at both the intake manifold and inside the cylinder. At low speeds, intake manifold injection provides better fuel atomization, significantly reducing carbon buildup and minimizing cold-start vibrations. The downside? Higher vehicle cost and slightly less aggressive highway performance compared to direct injection. If you frequently drive long distances, go for direct injection; for mostly city commuting, dual injection offers more peace of mind.
Last time I accompanied a friend to choose a car, the salesperson emphasized this. Direct injection has a simple structure and cheap maintenance. If the high-pressure pump fails, replacing it costs just a few hundred bucks. It delivers direct power and high efficiency. Dual injection is more expensive because it adds an additional port fuel injection system, and manufacturers position it as more high-end, like the new Toyota Camry using it. But the benefits of dual injection are obvious: less white smoke during cold starts in winter, smoother engine sound, and about half a liter lower fuel consumption compared to direct injection. In the long run, dual injection is more advanced, and the higher resale value is quite important.
From a car maintenance perspective, direct injection engines have the fastest spark plug fouling, requiring frequent use of gasoline additives to prevent clogged fuel injectors. Port and direct injection systems have significantly less carbon buildup in the cylinders, but the port injection system requires more cleaning, with maintenance costs 20-30% higher than direct injection. According to our car club's statistics, over five years, port and direct injection systems save over 1,000 yuan in overall maintenance costs. Although each service is slightly more expensive, the intervals are longer compared to direct injection systems that constantly require carbon deposit treatment.
