Experimental Research On Diesel Injection Control Strategies Of A Dual-Fuel Engine Fuelled With Diesel And Natural Gas

Diesel/natural gas dual-fuel engines can maintain the same compression ratio with diesel, so that it can achieve the comparative thermal efficiency like diesel engines. Using natural gas can reduce oil consumption and reduce CO2 and soot emissions. Therefore, diesel/natural gas dual fuel engine is one of the main technical approachs to internal combustion engines fueled with natural gas. In diesel/natural gas dual-fuel engines, the control strategy of the diesel fuel injection has an important influence on the combustion and emissions, therefore the optimization of fuel injection control strategy is an important technical approach to optimize the combustion process and achieve high efficiency and clean combustion. In this paper, we take the target to meet State V emissions regulations using simplified after-treatment and conduct experimental studies of the proportion of natural gas replacement ratio and injection control strategy optimization.This study was carried out on a dual-fuel diesel/natural gas engine modified from a heavy-duty diesel engine equipped with common rail injection system. First we investigated the effect of different natural gas replacement ratio on diesel/natural gas dual-fuel engine's performance and emissions. Study results showed that with the increase of natural gas replacement ratio, in-cylinder combustion characteristics change from diesel premixed and diffusion combustion to diesel premixed and diffusion combustion and natural gas lean premixed combustion ignited by diesel. Through the optimization of amount of diesel fuel and total excess air coefficient under the low load condition at low speeds, it can effectively reduce the THC, CH₄, and CO emissions, and achieve lower soot emissions, but NOx emissions increased slightly. Through the optimization of diesel injection timing, it can form more homogeneous charge in the cylinder, the engine's fuel economy and harmful emissions can be further improved.Then, the effect of fuel injection control strategy on combustion and emissions were investigated further. Research results showed that by employing early injection and higher total excess air coefficient under low load and low speed conditions, equivalent diesel fuel consumption was close to pure diesel fuel level, while THC, CH₄ and NOx ratio emissions were reduced, CO and soot emissions deteriorated slightly. By employing early fuel injection under medium speed small load combined with exhaust gas recirculation?EGR? and simultaneously through the optimization of diesel injection timing, the dual-fuel engine can both get better fuel economy and reduce harmful emissions and reduce the maximum pressure and rate of maximum pressure rise, which also helps improve diesel/natural gas dual-fuel engine life length. Under low speed medium load conditions, it requires the use of large scale pilot injection control strategies by optimizing fuel injection timing and injection pressure to improve fuel economy and reduce harmful emissions and emissions have the potential to meet State V by employing MOC?Methane Oxidation Catalytic? after-treatment.In conclusion, by using different natural gas replacement ratio and the optimization of injection control strategy under different operating conditions, diesel/natural gas dual-fuel engines have the potential to simplify after-treatment to meet State V emissions standard. This study laid foundation for developing diesel/natural gas dual-fuel engine.