Unintended Consequences Drive GDI Engines to Your Shops - Part 2
Recap and addendums to Part 1 (for details including sources, see Part 1 in the May 2016 issue of National Oil and Lube News):
• Gasoline direct injection (GDI) engines differ from previous engines in many ways that change their repair process and maintenance program. This becomes critical because, due to emissions and Corporate Average Fuel Economy (CAFE) mandates, engine manufacturing turned to GDI engine technology. These engines now appear in shops suffering from unintended consequences as they age.
• Need-to-know: Many modern vehicles powered by GDI engines are showing up in service departments with mysterious complaints. Diagnosing and remedying these engines’ issues early is important. Problems can affect engine performance in as little as 3,000 miles. Neglected treatment may require a costly upper-end teardown or vigorous mechanical cleaning to restore vitality.
• Potential impact on service provider reputation: GDI engine owners sometimes hear of unintended consequences and research to the point of believing they know more about their GDI engine than their service providers. Bad news travels like wildfire, so word-of-mouth on uninformed service providers damages reputations. Fortunately, customers return to the informed.
• Information in this series originates from sources that manufacture, test or report on GDI engines. With information and visuals available on public domains, I wish to motivate readers to perform your own research, especially since web photos often include make, model, mileage, etc. Rather than take our word for it, dig into the thousands of Society of Automotive Engineers (SAE) papers and articles listed by category in part 1.
• Why is this condensed training series important? In 90 percent of the motor industry, keeping up to date with changes in technology is beyond most workshop owners’ budget. Technicians could spend at least 10 working days of a month being trained.
Critical Carbon Deposit Engine Design Issues
SAE papers, including 2002-01-2659, identify deposits as the most critical engine design problem.
• Why? Deposits adversely affect drivability, power, performance, fuel economy, emissions, etc.
• How? Deposits interfere with air/fuel ratios, heat transfer, combustion, emissions, operation of mechanical components, etc.
GDI Engine Deposits Increase
SAE paper 1999-01-3690 addresses the deposit problem with early GDI engines, “Early [gasoline] direct injection engines suffered from severe deposit problems, which could not be overcome at the time.”
SAE paper 1999-01-1498 adds, “In GDI vehicles, deposited engines were found to have increased hydrocarbon and carbon monoxide emissions and poorer fuel economy and acceleration.”
Today’s complex GDI engines (see figure 1) attempt to address deposit issues. But according to Consumer Reports, problems continue with expensive repairs.
GDI Exacting Requirements
To improve efficiency, GDI engines must meet exacting requirements including: precise fuel metering, precise fuel spray patterns and targeting and optimized atomization. (See figure 2) But as reported by professor Przemek Jamroz, of the University of Maine’s Mechanical Engineering Department, deposits interrupt these precise requirements.
AutoGuide.com’s article, “Should You Buy a Car with Direct Injection?” adds, “The biggest concern with [gasoline] direct-injection technology is with carbon buildup. Carbon buildup can create a lot of headaches in the long-term, with buildup being bad enough to damage the engine, reduce fuel mileage and affect performance.”
According to ASNU, “[GDI] engine performance slowly deteriorates. It’s only a matter of time before the vehicle needs to go in to the workshop for maintenance and repair.”
How Deposits Form
Running engines are cooled by intake airflow and evaporating fuel. SAE paper 2002-01-2660 reports that at each engine stoppage, fuel residues remain, and SAE paper 2001-01-2030 adds that with no cool air and evaporating fuel, heat rises to its highest after 15-30 minutes. According to SAE paper 2001-01-1202, with engine stoppage heat, light fuel molecules evaporate but heavy olefins and aromatics (sticky, waxy substances needed to give fuel its energy) remain, oxidize and polymerize and form sticky coating of gums, varnish and resins.
As reported in SAE paper 902105, each engine stoppage produces a hot soak, and these sticky coatings build up and bake into thick, hard carbon deposits.
How We Drive
The DOT’s Federal Highway Administration Study reported in the US:
• 80 percent of cars start at least three times per day
• 63 percent of trips are under 20 miles
• 57 percent of driving is in stop-and-go traffic
So US driving produces deposit-forming conditions.
Typical Driving Impacts GDI Engine Deposits
SAE papers 1999-01-1498 and 200-01-2856 report that with driving cycles “representing a realistic mix of driving conditions (idle, urban, highway), engine fuel system deposits, including specifically those on intake valves, combustion chambers and injectors, are formed in higher amounts in the GDI engine than in the PFI engine.”
Parts one and two of this series lay the foundation of why GDI deposit review is critical to service provider success by reporting research on how deposits form and their impact on engine performance and maintenance needs — especially GDI engines that, according to Underhood Service, “Today’s [GDI] engines operate on a ragged edge between optimal efficiency and a misfire. There is not much room for error like hot spots in the combustion chamber or a worn spark plug.”
Future articles in this series will address GDI engine component service opportunities, starting with the throttle body plate and moving downstream. We’ll end the series with my report on indications of a trend in automotive and light truck engine technology.