Lubricant requirements to meet future engine technologies for India’s BS VI and fuel economy mandate
Compiled from staff reports
During the 10th International Symposium on Fuels and Lubricants (ISFL-2016) held in Delhi, India, in April, two most discussed topics were the forthcoming emission norms of BS VI, which is equivalent to Euro VI, in 2020 and the fuel economy mandates for passenger cars which start in April 2017 and will get tougher in 2022. India is also in the process of drafting fuel economy norms for heavy-duty trucks and buses, which may come up in the same time frame.
In his plenary lecture, Rajendra Petkar, head of Power Engineering, Tata Motors, viewed future regulations as an opportunity as well as a challenge for Indian OEMs to introduce cost-effective technologies for automotive engines. He talked about the rapid growth in India’s transport sector, driven by the increased rate of urbanisation, improved road infrastructure and higher disposable income among urban dwellers.
Petkar projects 11-13% compounded annual growth rates (CAGR) for vehicles in various categories over 2012-2021. There are several legislative demands in addition to customer preferences that an OEM has to meet. These include emissions regulations like BS VI in 2020, carbon dioxide (CO2) and fuel economy; noise, vibration and harshness; safety, comfort, performance and others. As emissions and on-board diagnostics limits become stringent in India, Petkar observes that there will be a need to spend considerable efforts in making engine management systems more robust. While development time available to OEMs is shorter moving from BS IV to BS VI than the time that was available for transitioning from BS III to BS IV, the demand for engine calibration efforts, control sensors and actuators will grow manifold.
At the same time, fuel economy/CO2 norms have been mandated based on weighted average performance. Fuel economy norms will be implemented in two phases – stage one in 2017 and stage two in 2022. Petkar observes that while India is open to renewable fuel choices, in practice, fossil fuels (liquid/gas) dominate the transport sector. The number of engines running on dual fuels and biofuels is very limited in India, while other carbon-free fuel options are still in the R&D stage. Every type of fuel has its own characteristic emission profile, alternative fuels being better on CO2 and particulate matter (PM) emissions. The difference on tailpipe emissions narrows down with the use of aftertreatment catalysts.
Petkar discussed many changes being developed for engines, including the ever-increasing injection pressures from 1,600 to 2,600 bar, higher application of two-stage turbochargers, variable-geometry turbochargers, external waste gate achieving pressure boost greater than three times the normal, engine thermal management with exhaust throttle drive, exhaust gas recirculation (EGR), intake throttle drive low pressure EGR, high efficiency EGR coolers and low swirl combustion to reduce PM.
All these hardware changes will be seen in BS VI engines, and yet will fall short of meeting BS VI emission norms without an elaborate aftertreatment catalyst system consisting of diesel oxidation catalysts, diesel particulate filter (DPF), selective catalytic reduction (SCR) and ammonia slip catalysts tuned to various applications and duty cycles. DPF regeneration in real-life Indian driving conditions is a challenge and several strategies will be tried, based on low- or high-temperature regeneration, with or without assistance from 7th injector or post injection, which are used to raise temperatures to facilitate DPF regeneration.
Aftertreatment systems on BS VI engines will necessitate Low SAPS (sulphated ash, phosphorus and sulphur) oils. Over the years, lubricants have been upgraded to match engine requirements. For example, when EGR systems and retarded injection were introduced to reduce NOx (nitrogen oxides) levels, the then current API CH-4 oils were found lacking in soot control handling and API CI-4/ CI-4 Plus oils were introduced. Both SCR and DPF in new generation engines are susceptible to blockage and poisoning to varying degrees; therefore, API CJ-4 specifications with restrictions on sulphated ash, phosphorous and sulphur were introduced. Fuel economy norms coupled with BS VI in India will need oils beyond API CJ-4. Perhaps Indian OEMs will try API CK-4/FA-4 oils, which will be available for licensing in December 2016. Besides these new heavy-duty engine oil performance levels, Petkar emphasised that Indian OEMs expect five key enabling roles from a lubricant: 1) increased oil drain intervals, 2) fuel efficiency benefits, 3) reduced oil consumption, 4) compatibility with exhaust aftertreatment systems, and, 5) compatibility with alternative and renewable fuels.
Lubricants with longer oil drain intervals have a smaller environment footprint and are cost effective for customers. Oil formulations should consider varying driving patterns and geographical conditions to deliver longer drain intervals, while protecting engines from wear. Fuel economy can come from engine oils through well-established routes of low viscosity oils, fortified with friction modifiers. Four key areas in an engine where friction dominates are the valve train, piston and liner, oil pump and crankshaft. Low viscosity can help reduce friction in all these areas, but OEMs’ concern with increased wear has to be addressed. The higher cost of a well-balanced fuel-efficient engine oil should make economic sense to the end user. Speaking on oil consumption, Petkar observed that besides selecting low volatility base oil components, optimum viscosity also has a key role, as higher viscosity oils form thicker oil films, resulting in higher evaporation loss.
Oil compatibility with aftertreatment systems is very important today, he said. Therefore, low SAPS oils are a must. Low sulphated ash should be achieved in lubricant additives, without impairing the lubricant’s oil drain capabilities. Low sulphur oil formulations can be achieved by using Group III base oils or by changing additive chemistry. Low phosphorous oils are needed without sacrificing wear protection.
Compatibility with alternate fuels is also important, as a mix of ethanol or biodiesel and the use of compressed natural gas (CNG) will increase. Each brings a set of different requirements for the engine oil. Petkar emphasised that engine oils for alternate fuel engines should be able to withstand higher levels of oxidation and nitration, protect against corrosion, prevent phase separation and handle high amounts of fuel dilution without lowering oil drain intervals.
Friction-modified oils and other topics
Other presentations at ISFL2016 covered friction-modified oils and other relevant topics.
The oil industry has always strived to develop bench-scale friction tests that correlate with ASTM Sequence VI, a test method that measures the effect of engine oil on the fuel economy of light-duty engines, to screen various oil formulations. Italy’s Eni Research Centre presented a methodology where the Stribeck friction coefficient (SFC1) for fresh oil under elasto hydrodynamic lubrication traction is measured and SFC2 is measured for the oil aged in a 168-hour oxidation test. These were shown to have good correlation with ASTM Sequence VID for organic friction modifiers.
Retaining the frictional advantage of a fresh oil formulation over the oil’s lifetime has been of great concern to oil formulators. Vanderbilt Chemicals showed the effects of using organo-molybednum and organic friction modifiers (FM) in a low viscosity SAE 0W-20 oil. Vanderbilt stated that organo-types are physically absorbed, while molybdenum-types are chemically reactive. However, a synergetic effect was observed when combining organic FM with Mo-FM, both in fresh oil and in aged oils. Different MoDTCs have similar performance in new oils, but vary in their retention of frictional properties in aged oils. The method of synthesis and composition play a crucial role in retaining friction after ageing. It was also emphasised that consumption of anti-oxidant additives has an influence on the performance of friction modifiers as engine oil is aged. Also, forming tribofilms with low intrinsic coefficient of friction is difficult due to the presence of various types of surface-active additives in a formulation.
The Indian Institute of Petroleum (IIP) in Dehradun presented the case of hexagonal boron nitride (Hex-BN) micro-particles as friction-reducing additives. IIP reported a significant reduction in friction to the order of 40% for mineral oils blended with functionalised Hex-BN micro-particles at higher loads in a four-ball tester. The enhanced anti-friction behaviour of Hex-BN micro-fluid can be attributed to the formation of efficient boundary films by Hex-BN particles, as revealed from Scanning Electron Microscopy and Energy Dispersive X-Ray analysis. Hex-BN has a lamellar crystalline structure, similar to graphite and molybdenum disulfide (MoS2). Because of its lamellar structure, Hex-BN has been beneficial in reducing friction and wear between contacting surfaces. However, its application in liquid lubricants has been hindered due to the poor dispersion stability of macro-size particles. In IIP experiments, Hex-BN micro-particles were functionalised by selective inclusion of long alkyl chains on the surface of the Hex-BN particles by octadecylamine through boron and nitrogen linkages. This resulted in a stable dispersion of micron-sized of µ-Hex-BN particles in the micro-fluids.
Chevron Oronite discussed the impact of lubricants for fuel economy in heavy-duty applications. Although lubricants may make a small contribution of about 2% fuel efficiency gain, they do not require any hardware changes. It was observed that in Heavy-Duty Federal Test Procedure (HD-FTP) cycles, operating temperatures have a large impact on fuel economy. In the cold phase of FTP, an SAE 10W-30 oil gave a 1.6% improvement in fuel economy compared to an SAE 15W-40, while in the hot phase, the difference was only 0.9%. The fuel economy advantage of the 10W-30 oil over the 15W-40 is highest in HD-FTP, followed by World Harmonized Transient Cycle (WHTC) and Ramped Mode Cycle (RMC). It was also observed that by changing high temperature high shear viscosity (HTHSV) from 4.2 to 3.0 cP (centipoise) about 1.2% fuel economy was observed in WHTC. Also 5W, with the lowest base oil blend viscosity, offers the lowest fuel consumption. At 3.6 cP, the brake specific fuel consumption (BSFC) difference between 15W and 5W for an XW-30 is 0.5%. Oronite demonstrated that by optimising viscometrics and additive chemistries, fuel economy advantages can be maximised, as well as retained, till the next oil drain period in modern heavy-duty engines.
Afton Chemical presented a holistic view of fuel economy solutions from lubricants. Since the 1980s, engine horsepower has steadily been rising, with a very slight increase in engine weight. Fuel economy suffered in 1985 to 2000 as new emission norms were brought in and OEMs struggled to get the right solutions. Since 2005, as emission technology matured and as several countries brought in fuel economy norms along with emissions legislation, OEMs started introducing more efficient engines. This trend is going to continue, with the greatest impact to be seen in U.S. vehicles from 2020 onwards.
Afton said that Volkswagen’s Golf 2015 model achieved a fuel efficiency above 35%, while the engine delivered 48% more power compared to the Golf 1997 model. The engine size had to be reduced by 15% and the vehicle became 23% heavier. Volkswagen also lowered the viscosity of the engine oil from SAE 10W-40 to 0W-30 in the Golf 2015 model. Challenging fuel economy targets required complex and integrated solutions, whereby engine oils were seen as an enabler to certain engine technologies. Lubricants will need to be balanced for viscometrics; friction modifier additives and lubricant formulations will have to be optimised.
A good correlation was seen between the fuel economy results of real world ageing of oil vis-a-vis ageing of oil in ASTM Sequence VID. Afton has standardised a Continuous Ageing Fuel Economy (A-CAFE) test to predict real world fuel economy. It is a composite test of four standard test cycles, run over a 90-km. chassis dynamometer test. A–CAFE test results had a good correlation (R2 =0.98) with the fuel economy data shown on EPA fuel economy stickers. A very good correlation was seen for 0W oils between HTHS viscosity and fuel economy; the lower the HTHS viscosity, the higher the fuel economy.
Adeka discussed the fuel economy performance of MoDTC additives in a low-sulphated ash passenger car diesel engine oil, which are needed for compatibility with DPFs. While low viscosity oils have a better correlation with friction torque at high engine speeds, MoDTC has good fuel economy correlation in both high and low engine speeds even in low-viscosity and low-sulphated ash oils. This combination can be a good solution to achieving fuel economy in passenger car diesel lubricants, Adeka said.
Mak Lubricants presented a study where moly-based lubricants, even in higher viscosity grades like 10W-40, produced better coefficient of friction than 10W-30 oils without moly in the high frequency reciprocating rig test, and even the wear scar diameter was small.
Croda presented the case of polymer organic friction modifiers (PFM) for minimising wear and friction in diamond-like carbon (DLC) surfaces. PFM is shown to give lower friction and wear than glycerol mono oleates in DLC coating surfaces. However, PFM has to be matched with the type of DLC coatings.
Mahindra presented a study on fuel economy effects of engine oils and the effects of friction modifiers in sport utility vehicles and light commercial vehicles engines. The study included Euro IV common rail direct injection engines in three-power ratings. Fuel economy evaluation methods included motoring torque method, driving cycle simulation on a transient engine test bed and chassis dynamometer. A good correlation between motoring torque test and chassis dynamometer was seen. Mahindra observed that a 10% decrease in HTHS viscosity makes a significant impact on fuel economy. Friction modifier chemistry and its interaction with additives in a lubricant formulation has an impact; the fuel economy advantage was seen in one friction modifier only, while no fuel economy advantage was seen in other FMs.
The need for field trials
The relevance of field trials is changing, in an ever-changing global market. In another presentation, Afton Chemical discussed methodologies for conducting driveline field trials. Today, field trials are necessary for several OEM approvals. They reflect real world driving conditions, but these involve high costs, man-hours and the risk of things going wrong midway in the trial. In the drive train, traditional OEMs such as GM, ZF, Ford, Volkswagen, Volvo, Caterpillar, Daimler and John Deere are going beyond traditional markets to new markets and facing competition from new OEMs such as Tata, JCB, Mahindra, Hero, FAW, Toyota, Dongfeng, Komatsu, Jatco, Chery, Hyundai and others. Effectively, the density of OEMs in all markets has increased.
As a result, a great diversity in product design is being seen in all markets. Before1990, there were only two primary designs for transmissions: manual transmission and step-type automatic. But after 1990, several designs became available such as continuously variable transmission, torrodial, automatic manual transmission, dual clutch transmission, hybridisation and electric. With this diversity, the number of OEM specifications, each requiring their own test, has grown significantly. More than 100 specifications exist today for driveline transmissions, with very little overlap in terms of tests. A market general universal tractor transmission oil will have to meet 11 specifications of key OEMs and that means about 200 tests that the oil has to pass. Afton’s experience shows that OEM specifications are too severe and at times may even lack correlation with the field; hence, invariably OEMs might include a field test as well. Field testing is therefore important in instilling confidence in the product. The most cost-effective way is to combine field trials of engine, driveline and axles as these are usually long trials. While the industry tries to pre-screen formulations or rely upon predictable tools for field performance, field trials are likely to be around for quite some time and we need to learn to do them cost effectively.
Looking at the engine oil presentations in ISFL-2016, it is quite evident that the Indian lubricant market is gearing up to provide fuel-efficient and high-performance low SAPS lubricants to enable Indian OEMs to meet BS VI norms in 2020 and also help them meet fuel economy mandates. It faces many costly roadblocks, however, such as the multitude of tests which are required to get OEM approvals.