Direct Injection Spark Ignition Engine Deposit Analysis: Combustion Chamber and Intake Valve Deposits

The delicate balance between global supply and demand for energy, in conjunction with environmental concerns related to burning fossil fuels, have resulted in vehicle designs that stress higher fuel economy. Among new engine designs is Direct Injection Spark Ignition, or DISI, which employs a more precise fuel metering system and is designed for combustion at higher compression ratios than Port Fuel Injection (PFI) engines. As a result, the performance of DISI engines can easily be altered by the presence of carbonaceous deposits on intake valves and in the combustion chamber.

In this study, the characteristics of these deposits have been investigated using elemental and thermal analytical techniques. Deposits from intake valves and combustion chambers have been collected from various DISI engines (both older and more modern ones). We have found that both fuel and engine lubricant contribute to the composition of deposits, and in particular:

• DISI intake valve deposit compositions consist of 10% (by weight) or higher non-carbon (inorganic) elements, of which Ca, Mo, Zn, P and S are dominant. The amount of these inorganic elements in the DISI engine intake valve deposit is at least one order of magnitude higher than in the PFI intake valve deposit.
• Thermal and elemental analysis data shows that significant differences exist in deposit volatility and its amount of inorganic components between combustion chamber deposits produced from Group III base oil (lower) and PAO (Poly-Alpha-Olefin) base oil (higher). No correlation was observed between lube oil sulfated ash value and elemental composition of deposits.
• Elemental composition of combustion chamber deposits is not significantly changed by the presence or absence of the fuel additives studied.
• The inorganic composition of DISI engine combustion chamber deposits show no significant differences when compared with PFI engine combustion chamber deposits.