How Dual-Fuel™ Works
The Diesel Engine
Diesel engines work on the principle of compression ignition. Air is first drawn into a cylinder where it is highly compressed – far more so than in a petrol/gasoline engine. It is this high ‘compression ratio’ that makes a diesel engine more efficient than its counterpart.
Diesel fuel is injected into the cylinder at high pressure, near the point of maximum compression. The combination of diesel fuel, and heated compressed air within the cylinder, results in ignition.
The fuel and air combination burns rapidly, increasing pressure and temperature, driving the piston back down the cylinder with great force. This sudden release of energy generates the power of the engine.
With Dual Fuel™ there is no change to the basic architecture of the diesel engine – or to the principle of diesel combustion. The engine itself is virtually unaltered, but for the addition of a gas injection system and an externally-fitted ECU. The Dual-Fuel™ in-cylinder temperatures and pressures remain within the limits of pure diesel operation, so the converted engine operates within the parameters of the original engine.
In a Dual-Fuel™ engine, however, the diesel fuel injector works like a liquid spark plug. Highly pressurized, it ignites a mixture of compressed gas and air in the cylinder, with natural gas comprising as much as 90 percent of the overall fuel mix (for more see link here to Dual-Fuel Vs Spark Ignition).
Tests have shown that the addition of Dual-Fuel™ components do not affect the base engine’s robustness or durability. And a quick and economic return to pure diesel at the end of ownership, ensures that residual values are not compromised.
Engine System Hardware
Dual-Fuel™ Electronic Control Unit (ECU)
- Controls/Interfaces with engine OEM’s ECU
- The Hawk™ ECU – a new generation in Dual-Fuel™ control
Turbocharger Air Bypass (TAB)
- Fast and accurate control of air-fuel ratio
- High performance actuators
Gas Injection System
- Electronically controlled gas injectors installed in modified air inlet manifold
Dual-Fuel™ Control System
The new generation Dual-Fuel™ ECU – the Hawk™ – was developed in 2007 and is now being applied to both Genesis and C-15 interfaced systems from Clean Air Power. The Hawk™ is a powerful and robust controller, with ECU hardware supplied by Mototron Inc with industry-standard software, engineered by Ricardo.
The Hawk™ meets or exceeds OEM standards for robustness and operation, providing the ideal platform for heavy-duty, stand-alone, retro-fit systems or OEM-interfaced installation.
The development of the Hawk™ is illustrated in the Technical paper “Development Of The Hawk™ Advanced Dual-Fuel™ Engine Management System to Enable the Use of Natural Gas in Today’s Heavy-Duty Vehicles” presented at the IANGV 2008 conference in Rio De Janeiro.
Natural Gas Injection
Clean Air Dual-Fuel™ injectors are controlled by pulse-width modulated signals from the ECU. The signals are based on manifold pressure, charge air temperature, gas pressure, gas temperature, and fuel mapping, providing the best combination of high efficiency and low emissions.
All Dual-Fuel™ engines will run with either Compressed Natural Gas or Liquefied Natural Gas. Super-cooled LNG requires vacuum-insulated, low-pressure fuel tanks which take up less space than compressed CNG gas tanks. CNG tanks are three times larger than LNG tanks for the same basic fuel capacity.
Either fuel delivers the same engine performance.
CNG and LNG
The ability to use both forms of natural gas is essential for commercial success in an ever-growing and changing market. As a complement to the development of Dual-Fuel™ technology, Clean Air Power pioneered vehicle systems for storing and delivering CNG and LNG.
Working closely with manufacturers and Dual-Fuel systems fitted to their vehicles around the world, the company has built on this expertise. Today Clean Air Power delivers hardware from specialist component suppliers that includes LNG tanks, CNG tanks, premium industry-standard fitting and fixtures.
Natural Gas Quality
The quality and composition of natural gas is an issue for the transport industry. The presence of heavier gases, such as ethane and propane in the mix, can lead to combustion knock in the engine. If left unchecked, this phenomenon can lead to engine failure.
Today, satisfactory gas composition cannot be assured as there are no national standards regulating gas quality. However, Clean Air Power has developed a countermeasure to protect the engine from poorer quality gas. The system uses an engine-mounted knock-sensor, integrated into the electronic control system. If a combustion knock is detected, the system automatically adjusts the operating mode of the combustion, immediately preventing knock, thereby protecting the engine.