Differences Between Direct Injection engine and Electronic Injection engine in Excavators

I often hear some experienced workers saying, “Your excavator engine is direct injection, while your excavator engine is electronically injected.” Those who have been in the industry for many years know the distinctions between direct injection and electronic injection. But for those of us who are new to the field, how do we distinguish between direct and electronic injection? Today, I will share the differences between them.

1. Throttle Control Mechanism

The direct injection engine is controlled by the engine speed; it relies on manual throttle adjustment via a dial and the selection of power modes through a physical switch to regulate throttle opening. The overall structure is relatively simple.

In contrast, the electronic fuel injection engine has a controller that detects various signals: throttle opening angle, power mode switch, engine speed, fuel pump pressure, operation valve pilot signals, excavator working modes, and temperature signals such as water and oil. The ECU (Electronic Control Unit) determines the optimal throttle position (the engine’s optimum speed) based on the driver’s input, different power modes, working conditions, load states, and operational conditions. Additionally, the ECU can control the rate of throttle opening changes (the speed at which the throttle transitions from one angle to another), allowing the engine to perform at its best.

For the electronic fuel injection engine, throttle control is no longer a simple manual switch selection. Instead, it involves intelligent analysis of load conditions, complex automated control, and extensive reliance on software for most functionalities. The controller processes the data, sends corresponding control signals to the throttle drive motor, and performs throttle control operations.

2. Injector Operation

The direct injection engine technology is mature and has a high residual value (i.e., the value of a direct injection excavator at the end of its usable life), making it relatively better at retaining value. However, a drawback is that due to the high operating speed of diesel engines, the fuel injection timing is very brief, only a few milliseconds. As the time and pressure within the high-pressure fuel line change, variations in diesel pressure due to its compressibility and inconsistencies in the supply lead to significant differences in actual injection conditions compared to the scheduled plunger fuel supply.

Occasionally, pressure fluctuations within the fuel line after the main injection can cause a re-increase in pressure, leading to secondary fuel injection. This is problematic because secondary injection cannot be completely combusted, increasing the emissions of hydrocarbons and smoke, and thus raising fuel consumption.

Furthermore, the residual pressure in the high-pressure fuel line changes after each injection cycle, which can easily lead to unstable injection. Experienced drivers indicate that this instability occurs most frequently when the engine is at low RPMs. In severe cases, not only is the fuel injection uneven, but there may also be random instances where injectors do not spray at all.

The common rail electronic control fuel injection technology for diesel engines has advanced significantly in recent years, overcoming many of the traditional diesel engine’s main flaws. The essence of common rail technology is to separate the generation and process of injection pressure within a closed environment consisting of a high-pressure fuel pump, pressure sensors, and a computer control unit (ECU). Simply put, the high-pressure pump delivers high-pressure fuel to a rail, which maintains a consistent pressure level. The ECU determines the necessary injection pressure and timing based on load and speed signals, controlling the opening of the injector accordingly.

Its features include the ability to freely control the injection quantity, pressure, and rate of injection (speed), as well as the exact timing of injection. By accurately controlling the oil pressure within the common rail, the pressure in the high-pressure line becomes independent of the actual engine speed, significantly reducing the pressure changes traditionally associated with diesel engines.

3. Repair and Maintenance Differences

In practical user experiences, direct injection diesel engines typically have lower maintenance costs. They produce high torque during operation, making them powerful and suitable for the average Chinese user (who may use lower-quality diesel). The main drawback is that, due to the generally low quality of domestic fuel, diesel supply issues can easily lead to increased carbon buildup in the cylinders, resulting in power loss, lower RPM, and difficulty starting the engine.

Electronic fuel injection diesel engines can achieve excellent compatibility with hydraulic systems. The downside is that they require high-quality diesel, and the later-stage maintenance costs are higher compared to direct injection engines. Severely damaged components often need to be repaired by the manufacturer.

4. Energy Efficiency and Environmental Impact

Direct injection engines have a strong adaptability to fuel quality, but they cannot combust fuel completely, leading to higher fuel consumption and poorer environmental performance. Electronic injection engines require relatively higher fuel quality, allowing for more complete combustion and better fuel efficiency and environmental outcomes.

These are some of the key differences between direct injection and electronic injection engines.

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