Diagnosis and Prognosis of Fuel Injectors Based on Control Adaptation

Diagnosis and Prognosis of Fuel Injectors based on Control Adaptation Azeem Sarwar1, Chaitanya Sankavaram2, and Xiangxing Lu3 1,2,3 Vehicle Health Management Group, Vehicle Systems Research Laboratory, General Motors Company, 30565 William Durant Blvd, Warren, MI, USA [email protected] [email protected] [email protected] ABSTRACT 54.5 mpg by 2025 (Ferguson & Kirkpatrick, 2015). Follow- ing the stricter requirements, the emission level of current in- Spark Ignition Direct Injection (SIDI) technology enables ternal combustion engines has decreased to about 5% of the better fuel economy and tail pipe emissions in vehicles emission levels that were prevalent 40 years ago (Ferguson & equipped with gasoline engines. The SIDI technology de- Kirkpatrick, 2015). pends on the ability of the system to deliver fuel at high pressure directly into the combustion chamber, hence making the Up until 1990s, Port Fuel Injection (PFI) Engines reflected fuel injectors key subcomponents. Reliable performance of state of the art for production gasoline engines (Çelik & fuel injectors is vital as it directly relates to the operability of Ozdalyan, 2010). Advancement in computer-based con- the vehicle, and hence customer satisfaction in case of failure. trol made it possible to deliver gasoline precisely through It, therefore, becomes very important to devise a scheme that solenoid-based fuel injectors, just upstream or at the back of can effectively diagnose and prognose such a component. In each cylinder’s intake valve. The fuel then mixes with the this article, algorithm development for diagnosis and a path- incoming air, and gets pulled into the combustion chamber way to prognosis of fuel injectors is presented. We do not when the intake valve opens. Combined with oxygen sen- propose any additional sensing capability, and make use of sors mounted on the exhaust, the computer is able to achieve what is available in most of the production vehicles today very accurate control of desired air-fuel ratios. PFI engines, across the industry. In particular, the control adaptation of however, still could not overcome the following challenges fuel control and the associated diagnostics that are mandated (Takagi, 1998): by regulators are employed to generate schemes for fault de- • degradation in fuel economy due to pumping losses dur- tection, fault isolation, and fault prediction. Results are pre- ing part load operation, sented from vehicle test data that allow development of such a scheme for fuel injectors. • knock limited output performance, • wall wetting or formation of fuel puddle in the manifold 1. INTRODUCTION during cold engine start resulting in excessive Hydrocar- bon emissions. Stricter emission regulations and increasing fuel economy requirements have been amongst the key driving forces that Increasingly tighter fuel economy and emission regulations have led the automotive industry to constantly improve the prompted the herald of spark ignition direct injection (SIDI) efficiency of gasoline engines, and also innovate to reduce engines into production. In SIDI engines, fuel is injected di- harmful exhaust gas emissions. Corporate Average Fuel rectly inside the combustion chamber at high pressure during Economy (CAFE) is the primary vehicle mileage standard in the compression stroke, reducing wall wetting and hence im- the United States. From 1990 to 2010, the CAFE standard for proving cold start Hydrocarbon emissions. A pictorial differ- the passenger vehicle remained fixed at 27.5 mpg. However, ence of Port Fuel Injection and Direct Injection is shown in the CAFE standard has been changing rapidly in recent years, Figure 1. with its value reaching 35.5 mpg in 2016 and increasing to Direct Injection has many advantages (Zhao, Lai, & Harring- Azeem Sarwar et al. This is an open-access article distributed under the terms ton, 1999; Smith & Sick, 2006), for example, it: of the Creative Commons Attribution 3.0 United States License, which per- mits unrestricted use, distribution, and reproduction in any medium, provided • reduces throttling loss of the gas exchange by stratified the original author and source are credited. and homogeneous lean operation, 1 ANNUAL CONFERENCE OF THE PROGNOSTICS AND HEALTH MANAGEMENT SOCIETY 2017 Figure 1. Schematic of Gasoline Port Fuel Injection and Figure 2. Production Forecast of Direct Injection & Multi- Gasoline Direct Injection Systems point Fuel Injection Engines in North America (Source IHS) • enables higher thermal efficiency by stratified operation vehicle programs and selected vehicle components in Model and increased compression ratio, Year 2016 under its strategic initiative to develop Vehicle Health Management (VHM) technologies. The OnStarTM • decreases the fuel consumption and CO emissions, 2 Proactive Alerts service is designed to provide early warn- • lowers heat losses, ing to customers in case a component failure is impend- • enables fast heating of the catalyst by injection during ing, thereby turning emergency repair services into scheduled the gas expansion phase, maintenance events. More advanced VHM technologies are • increases performance and volumetric efficiency due to to be developed under this initiative. The fuel delivery sys- cooling of air charge, and tem of an SIDI engine is critical to a given vehicle’s drive- ability, and fuel injectors are amongst its key components. It • enables better cold start performance. is, therefore, highly desirable that their failure is prevented, Compared with conventional Spark Ignition engines, SIDI and a timely warning be issued in case of imminent failure, engines utilize lean-burn-based stratified charge mixture, in- so that they can be timely serviced. In addition, billions of creasing fuel economy by up to 25%, depending on the test US dollars are spent by the automotive industry towards cov- cycle (Zhao et al., 1999). The SIDI engines also provide ering the warranty costs and most of the fault identification a 10% improvement in power output while simultaneously and isolation techniques involve offline troubleshooting by reducing the cold start unburned HC emissions by approxi- the service technician based on the data available from the mately 30% (Takagi, 1998). SIDI engines have allowed the vehicle at that very instant (Lanigan, Kavulya, Narasimhan, reduction of pumping loss, knock, and intake port wall wet- Fuhrman, & Salman, 2011). Limited information sometimes ting, the resolution of which was a long-cherished wish of leads to erroneous parts replacements causing unnecessary in- combustion engineers. crease in warranty costs and customer inconvenience. Much of the on-board diagnostics today, especially related to power- There is an increasing trend towards the adoption of SIDI en- train, have been developed with a focus of meeting the regula- gines in the North American market. According to Informa- tor requirements and not so much from a service perspective. tion Handling Services (IHS), there is a decreasing trend in This article provides the development of prognostic technolo- the production forecast of PFI engines, and they are being gies for fuel injectors by detecting degradation in their perfor- gradually replaced by the SIDI engines. The total number mance with a focus to identify the correct problem by lever- of engines running on PFI technology will reduce down to 4 aging the historic data, and fixing it right the first time. The million by 2023, as compared to 13 million engines that will problem is quite challenging if the sensing ability is limited feature SIDI technology according to the production forecast to what is available in the production vehicles today with- generated by IHS (see Figure 2). Hence, more and more ve- out adding any additional sensing capability to aid our quest. hicles will be equipped with SIDI engines in the future. The No prior literature exists, to our knowledge, that provides any ability to deliver highly pressurized fuel directly into the com- development towards prognosis of fuel injectors for SIDI sys- bustion chamber is the key enabler for the SIDI engines. It tem. is, therefore, imperative that the fuel delivery system of an The article is organized as follows. Section II describes the SIDI engine can operate without failure. Failure in the fuel operation and control of SIDI high pressure fuel delivery sys- delivery system of SIDI engines can cause customer frustra- tem, and focuses on the operation and control of fuel injec- tions, costly road side assistance (including vehicle towing), tors. Section III describes the possible faults that occur in and negatively impact the perceived quality of the automotive fuel injectors along with experimental cases to study these manufacturer. faults. Section IV describes the fault identification, isolation, GM launched OnStarTM Proactive Alerts service on selected and prognostics algorithm that is developed based on the in- 2 ANNUAL CONFERENCE OF THE PROGNOSTICS AND HEALTH MANAGEMENT SOCIETY 2017 sights gained from Section III. We conclude the findings of orifice, ∆P is the pressure differential between the fuel rail our study in Section V. and engine cylinder during intake stroke, and the discharge coefficient Cd is given as: 2. HIGH PRESSURE FUEL DELIVERY SYSTEM DE- 2λ SCRIPTION Cd = Cdmax tanh (2) λcritic A typical SIDI system is shown in Figure 3 for a four cylinder application. In SIDI systems, gasoline is injected directly The dimensionless flow number λ is given as: into the combustion chamber. This requires gasoline to be s d 2j∆P j at high pressure which is achieved in two steps. First, the λ = h (3) in-tank electric fuel pump delivers fuel from the tank to the ν ρ inlet of the high pressure fuel pump. The high pressure fuel pump then compresses, and pushes the necessary amount of where, dh is hydraulic diameter and ν is the kinematic vis- fuel into the fuel rail, generating and maintaining the required cosity. pressure. The high pressure fuel pump increases the fuel rail pressure from a pump inlet line pressure of 0.3 to 0.5 MPa to a range of 1 to 20 MPa. Fuel injectors are connected to a common fuel rail and remove fuel from the fuel rail with each injection event, resulting in a decrease in fuel rail pressure.

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