Study On Control Strategy Of Start In An Electronic Controlled Gaseous LPG Port Injected Spark Ignition Engine

Under the stress of oil supply and consumption, plus environment protection, studies on electronic controlled gaseous LPG engine are of great significance in order to optimize components of power resources consumption. Nevertheless, as an alternative fuel for engine, LPG engine still has to deal with cold start problems. European Community is enforcing stricter and stricter vehicle emissions regulations. In addition to lower emissions requirement, test procedures are also updated. The first 40 seconds originally without taking emissions measurement now must be taken into consideration. Experiment data have shown that HC and CO emissions during cold start are about 50% up to 80% of all accumulated emissions during the whole test procedures. With employment of 3‐way catalyst converter, overall emissions can be drastically reduced. However, during cold start, 3‐way catalyst converter can not be lit off because of low temperature in exhaust system. So, as for LPG fuelled engines, study on control strategy during cold start is of importance for achieving low or ultra‐low emissions. This paper only covers control strategy for an LPG engine that has not been matched with a 3‐way catalyst converter. Start reliability, engine speed stability, and above all, transient air fuel ratio, HC and CO emissions are major concerns. Main work in this literature includes: 1. Reconstructed a Jetta electronic controlled 2‐valve engine into an electronic controlled gaseous LPG port injected engine with LPG injectors made by OMVL from Italy. 2. High‐speed data acquisition and reliable data storage are achieved by means of high‐performance PCL‐818HG data acquisition card and its PCLD‐8115 writing terminal board made by Advantech Co. Ltd. 3. This electronic controlled LPG injection system is developed upon a Jetta 2‐valve electronic controlled SI engine. Therefore, the originally‐equipped sensors and ignition module can be used directly in this LPG injection system. After considering hardware characteristics of the original sensors and actuators, signal processing circuits for sensor signals and driving circuits for acuators are designed. 4. Strategies for battery voltage compensation and electrical fuel pump control are designed. 5. Strategy for idle main throttle position control is designed with a fuzzy‐PID compound controller. When the deviation is large, fuzzy controller is activated. PID controller with intelligent I‐part is activated when the deviation is small. 6. Control strategy for LPG engine during cold start is developed. Initial throttle position and initial injection pulse width are determined in accordance with engine coolant temperature, optimizing engine startability and engine out emissions. Different control strategies during after start phase are developed for gasoline engine and LPG engine respectively. 7. Cold start experiments are carried out in LPG and gasoline engines at environment temperature 9℃, 15℃and 20℃respectively. The calibration software is developed by our team, which has functions of monitoring, data storage and real‐time adjustment of control parameters. Cold start experiments of gasoline engine and LPG engine are studied. Effects of Initial fuel injection pulse width, intial throttle position, injection width decremental gradient, throttle angle decremental gradient and other control parameters on transient air to fuel ratio, transient engine speed and transient emissions are studied. Experiment results show that: 1. The system designed in this paper can control the LPG engine reliably; hardware and software of the system is reliable. 2. Engine coolant temperature, oil temperature and intake air temperature have significant effects on engine cold start performance. As for 9℃, 15℃and 20℃cold start experiments, minimum lambda is 0.713, 0.729, 0.74 respectively in LPG engine and 0.684, 0.692, 0.712 respectively in gasoline engine. These results demonstrate that the mixture that LPG fuelled engine needs to start successfully is leaner than that of gasoline fuelled engine. Furthermore, the lower the temperature, the richer mixture engines need to start. It is true in both LPG and gasoline engine. 3. Under the environment temperature condition of 9℃, 15℃and 20℃, the ratio of the initial injection width to the pulse width when lambda rises up to 1 is 6.98,6.92,6.94 respectively in gasoline engine. As for LPG engine, the ratio is 2.5,2.46,2.36 respectively. These results show that LPG engine also has to need large amount of fuel to form rich mixture for cold start, same as the gasoline engine. However, the ratio in LPG engine is much smaller than that of gasoline engine because LPG is gaseous fuel and tends to mix with fresh air to form combustible mixture relatively more easily. As for gasoline engine, especially under cold condition, the wall film phenomenon is obvious and unavoidable. To build up the wall film during cranking and cold start, large amount of fuel is needed compared with LPG fuel. 4. Different after‐start control strategies are developed for LPG and gasoline engine, which limit the engine speed overshoot of LPG engine within 100r/min with respect to target idle speed and the transition period from start to idle phase is about 4 seconds. The speed overshoot of gasoline engine is limited...