Design and application of air to fuel ratio controller for LPG fueled vehicles at typical down-way
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This article presents an investigation of air–fuel ratio (AFR) controllers applied to liquefied petroleum gas (LPG) fuelled vehicles with second-generation LPG kits. When a vehicle is running on a down-way, fuel consumption tends to be rich because of the increased vacuum in the intake manifold. Therefore, an AFR controller was developed that can work based on a vehicle’s tilt sensor combined with an oxygen sensor. AFR controllers are employed to regulate injectors to form leaner mixtures. We tested the performance of AFR controller at a typical down-way of 10°, 15°, and 20°. As a result, the AFR controller was able to increase AFR value from an average of 14.5 (without controller) to 15.5–16.2, depending on the gear position and down-way angle. Furthermore, a greater of road slope was observed to have produced greater AFR. This AFR controller is very promising to be applied to vehicles operating in mountainous areas.
KeywordsLPG vehicle AFR controller Down-way
In the past few decades, environmental factors have become the main orientation in technological development, especially concerning health issues. In addition to the industrial sector, transportation is one of the sectors targeted to reduce global warming, air pollution and emissions [1, 2, 3]. Therefore, the design of vehicle technology needs to consider emission factors [4, 5]. From another perspective, there is also a potential global energy crisis and this call for the design of technology to improve fuel efficiency for new and operating vehicles .
Electric vehicles (EVs) and Fuel Cell Vehicles (FCVs) are very promising to reduce fuel consumption and emissions, even to zero value, in the future. However, the implementation of EVs and FCVs is constrained in developing countries due to uncompetitive prices and limited mileage . In EVs, the battery requires a long time to charge with high input power  while FCV is limited by infrastructure needed to produce hydrogen. In the medium term, hybrid vehicle (HVs) is a reasonable choice and it involves combining internal combustion engines (gasoline/diesel) with electric motors [8, 9]. However, this technology is also not yet widely accepted due to the relatively high total cost of ownership (TCO).
Therefore, in the short term, controlling air to fuel ratio (AFR) is an alternative method to reduce fuel consumption and emissions. This system has progressed rapidly, even with the use of proportional–integral–derivative (PID) for stoichiometric purpose . Neural networks as intelligent control systems have also been applied to control AFR with the concept of brain tissue . Several other studies have been conducted by processing signals generated by oxygen sensors , applying genetic algorithms , fuzzy logic controllers (FLC) [14, 15, 16], diagonal recurrent neural network (DRNN) , and brakes control system .
Moreover, other methods to reduce emissions have been researched to include the application of alternative fuels such as ethanol, methanol, compressed natural gas (CNG), and LPG [19, 20]. Ethanol produces good efficiency and reduces emissions, but it cannot be produced in large numbers except a country has a reliable policy on agricultural land for food and energy . Therefore, LPG is considered an alternative and choice of several countries due to many advantages such as high octane, lower exhaust emissions, and availability.
Research on several variables of LPG as an alternative fuel has been conducted by different researchers. For example, Morganti  conducted a study to test the research octane number (RON) and motor octane numbers (MON) for iso-butane, propylene, n-butane and propane, followed by observations of auto-ignition from a mixture of propane and butane. In another study, Chikhi  investigated CO, HC, NOx and CO2 emissions produced by 17 units of bi-fuel vehicle using LPG to replace gasoline and diesel. Moreover, it is also possible to control the sulfur and toxic gases produced by LPG vehicles to achieve better emissions [24, 25]. Other studies focus on iso-octane and air mixtures , performance characteristics of LPG, CNG and LNG vehicles , direct-injection application with lean combustion methods , and risk analysis of the safety of LPG-fueled cars .
Meanwhile, several research works have also been conducted on the control of LPG. In 2015, Erkus  developed an LPG control system to be applied in carburetor-based engines. The results of this study confirm an increase in engine performance and better exhaust emissions compared to the carburetor system. Others study, including the fuel cut-off method to cut off LPG flow to the engine during deceleration by controlling the solenoid on the vaporizer [31, 32], emission comparison using a control system on liquid phase injection (LPI) and direct injection (DI) , as well as the characteristics of injection duration and control [34, 35, 36]. This has led to the development of intelligent control systems to support fuel efficiency. However, the studies conducted have not considered the contours of the land, such as up-way and down-way. When a vehicle passes through a down-way, kinetic force, and gravity affect its movement. Meanwhile, when the vehicle accelerates on a down-way, the fuel is reduced or even cut off.
Furthermore, even though LPG kits technology is now equal to GDI technology, in fact, more LPG vehicles use second-generation LPG kits (vapor phase injection, VPI) without strict AFR and emission settings . With second-generation LPG kits, AFR stoichiometry is only obtained in partial conditions. When the vehicle accelerates in the down-way, the tendency for low AFR is greater than the high AFR. Therefore, we developed the AFR control system on LPG vehicles that pay attention to the slope of the road. This control system works based on the primary information from the tilt sensor.
2 Materials and methods
2.1 Vehicle specification
Bore × Stroke
78.7 × 77 mm
DOHC, 4 valves per cylinder
Maximum power output
77 kw @ 6000 rpm
135 Nm @ 4800 rpm
2.2 AFR controller
3 Results and discussion
3.2 AFR measurement
AFR measurement data
Speed gear position
Without AFR controller
With AFR controller
From Table 3 and Figs. 5, 6, and 7, the result shows that the greater slope of the road produced higher AFR. This indicates that the kinetic force and vehicle gravity can be used as input parameters to control the AFR. In previous studies [31, 32], the AFR controller system in LPG vehicles were applied based on decelerations with input parameters from engine, brake, and vehicle speed. In this study, the AFR controller developed has the ability to work on reduced road conditions at low vehicle and engine rotation speeds. Based on the data during observation, this AFR controller has a great potential to be applied to modified LPG vehicles that operate in mountainous areas, although this only makes a small contribution to areas with the majority of flat roads.
The results showed that the kinetic force, gravity, vehicle weight, and road slope have the potential to be used as input signals by the AFR controller to improve fuel efficiency. The AFR controller developed was able to increase the AFR value from an average value of 14.5 to 15.5–16.2, depending on the down-way angle while the gear position has no measurable effect. Furthermore, a greater slope of the road was observed to have produced greater AFR. In conclusion, the AFR controller has the ability to increase AFR and it is very suitable for modified LPG vehicles with first and second generation of converter kits that are not yet equipped with lambda sensors, especially for LPG vehicles operating in mountainous areas.
This research is part of an environmentally friendly vehicle development project at the Automotive Laboratory of Universitas Muhammadiyah Magelang. The researchers appreciate the technicians involved in this study.
Compliance with ethical standards
Conflict of interest
The author(s) declare that there is no conflict of interest regarding the publication of this article.
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