For example, Fords turbocharged EcoBoost V6 claims to deliver all the power of a naturally aspirated V8 but with the fuel economy of a V6. Another version, Mercedes-Benzs CGI BlueEfficiency engine with spray-guided direct injection, gets 10 percent better fuel efficiency yet can propel the C 350 sedan from a standstill to 100 kilometers per hour in just 6.2 seconds.

In a SIDI engine, gasoline is injected directly into the combustion chamber through a high-pressure fuel rail, rather than through a conventional port fuel injector. The fuel rail pressures are enormous (over 2,000 pounds per square inch) and create a denser charge that results in more powerful performance.

With so much power and pressure – and so much hope riding on them – can these engines get the wear protection they need from low-viscosity oils formulated with low SAPS (sulfated ash, phosphorus and sulfur) additive packages? The answer is yes, Infineum has concluded after a two-part study involving used oil analysis and a field trial.

Low SAPS formulations help to maximize the benefits of improved fuel economy and are compatible with the exhaust after-treatment devices that reduce emissions of SIDI gasoline engines, said Simon Chung, crankcase technology team leader, Singapore, for additives maker Infineum.

In a June 15 presenation to the ICIS Asian Base Oils & Lubricants Conference in Seoul, South Korea, Chung pointed out that spark ignition direct injection is not actually a new technology. Its been around for a number of years now, but it continues to improve.

In a conventional port fuel injection engine, the air in the fuel is mixed just before going into the combustion chamber, he said, whereas for a gasoline direct injection engine the fuel and gasoline is mixed inside the combustion chamber because the fuel is injected directly into the combustion chamber.

Some of the benefits of SIDI engines include low emissions, particularly at start-up, and of course better fuel economy. These benefits are due to the better atomization of the fuel directly in the combustion chamber before ignition, Chung explained, which results in better mixing and combustion.

That doesnt mean the technology is perfect, he pointed out. There are concerns with SIDI engines – one is that due to the combustion methodology, some soot-like particles can be produced, depending on the type of SIDI, methodology and engine, Chung said. And there are concerns that these particles will cause soot-induced abrasive wear. To address OEM concerns about this threat, Infineum designed a study to investigate the nature of these soot-like particles, and how they compare to soot formed in a conventional diesel engine.

While soot might not seem very hard or abrasive in conventional diesel engines, he noted, it can be quite damaging on a microscopic scale. They do get into the contacts, and if the oil films are thin enough, the soot can potentially give you soot-induced wear, Chung said. That is the concern with SIDI engines.

The first part of the study analyzed used oil samples from SIDI gasoline engines and diesel engines to compare the quantity and properties of soot particles that were generated in the oils. The data from this will help us to gauge if soot-induced wear is a likely mechanism contributing to wear in SIDI engines.

Infineum used thermogravimetric analysis to measure the amount of soot content. In the SIDI oil sample, we found 1.3 percent of soot-like particles, significantly lower compared to the diesel engine oil sample, which found 4.8 percent soot, more than three times as much.

The next step was to use transmission electron microscopy (TEM) to look at the soot structure. This method observed very few particles in the SIDI oil sample. Those seen were difficult to resolve and didnt appear to be normal soot structures, Chung pointed out. TEM revealed well-formed, clearly resolved soot structures in the diesel oil samples, with a degree of clustering and aggregation and agglomeration similar to previous experience.

The third analytical technique was X-ray photoelectron spectroscopy, which is designed to look at the surface composition of soot particles. For the SIDI oil sample, unsurprisingly, its mainly carbon and oxygen, and there are traces of additives such as phosphorus, sulfur and calcium – typical additives youll find in an engine oil, Chung said. In the diesel oil sample, youll find mainly carbon and oxygen on the soot, with traces of additives elements such as phosphorus, sulfur, zinc and magnesium.

So we believe the lower amount and limited structure of soot particles observed in the SIDI oil could result in less wear by abrasive mechanism, but further investigation will be required to understand this, he continued.

For the second part of the study, Infineum conducted a SIDI engine field trial to evaluate component and formulation effects. Its first objective was to demonstrate performance and confirm there was no harm from using low-viscosity-grade, reduced SAPS oils in SIDI engines. The second objective was to evaluate the performance effects of the formulation, in particular detergent type and phosphorus level.

Infineums field trial involved three candidate lubricant formulations – two SAE 0W-20s and one 5W-30 – on two vehicles each. The trial length was 60,000 miles, with oil drain intervals of 10,000 miles and oil sampling intervals of 2,000 miles. Infineums research center at Milton Hill, U.K., served as the test site.

Hardware measurements included cam chain length at the start, middle and end of the trial, and a standard engine rating at the end of the trial. In terms of crankshaft and bearings, and cam chain wear, the numbers there were very, very good – we saw not much wear at all.

Chung noted that the market and industry are trending towards lower-viscosity multigrade oils, such as SAE 0W and 5W, for improved fuel economy. Another trend is increasing performance requirements for both industry-wide and OEM lubricant specifications. The industry is also moving towards reduced SAPS formulations for compatiblity with exhaust aftertreatment devices, he added.

The result of those trends, according to Chung, will be increasing use of higher performing API Group III and Group IV (polyalphaolefin) base stocks to meet the viscometric and performance requirements of advanced engine lubricants. For the SIDI field trial, Infineums three formulations included one 0W-20, blended with Group III and IV base stocks; another 0W-20 also blended with Group III and IV base stocks but with a different detergent system; and a 5W-30 blended with Group III and the same detergent as the first oil. The two 0Ws each contained phosphorus at 0.05 percent; the 5W was slightly higher at 0.08 percent phosphorus, but that still met the limit for ILSAC GF-5 oils.

Chung reported there was no decrease in viscosity observed due to high fuel dilution or shearing of viscosity modifier. The oil analysis also observed no increase in viscosity due to oxidation, or high oil consumption due to problems with Noack volatility.

Finally, Chung pointed to oil analysis for wear metals with the samples. The samples showed iron concentrations at expected levels, and indicated no wear issues. The analysis also indicated very low levels of copper and lead in the oils, and showed no bearing wear or corrosion issues. And good repeatability could be observed in all the wear metals results between the pairs of oils.