Premium technology lubricants play an important yet often unknown role in keeping cogeneration units running effectively.

Gas engines with ever-higher demands

The quest for greater efficiency in cogeneration plants is never-ending. For the last 30 years, gas engine manufacturers have been consistently improving the performance of their products. The result is engines that are designed to be more economical and efficient, but also much more demanding.

It is important to realise that today’s gas engines are exposed to extreme pressures and temperatures, as much as four times higher than those in a diesel vehicle engine. In addition, engines are connected to heat exchangers to recycle the energy produced and to the catalytic converters required by increasingly strict anti-pollution standards. This complex arrangement with equipment sensitive to fouling from ash present in oil additives adds further integrity demand.

Today’s lubricants play a central role in cogeneration unit engine management – they help keep the well-oiled machinery running properly. But the characteristics of the oil used are important. An unstable total base number (TBN) or excess sulphated ash content in an oil product can result in expensive breakdowns with serious consequences – risks few facility operators are aware of.

Gas engine oil – a very technical oil

Gas engine oils are required to meet multiple challenges. They have to do the standard job of any oil – lubricating, preventing deposits and keeping the combustion chamber clean. Additionally, gas engine oil also must go the extra mile to deal with problems arising from the characteristics of biogas and variations in the quality of the fuel.

The oil must possess guaranteed thermal stability while controlling oxidation and offering good TBN retention. The oil has to neutralise acidity caused by the gas while also helping guarantee engine performance. The difficulty lies in balancing TBN stability with the sulphated ash levels in additives, as these two parameters are closely linked.

TBN stability – a crucial indicator

The basicity index, or Total Base Number (TBN), particularly TBN stability, is a very important technical characteristic of oil and a factor in which cogeneration facility operators should bear in mind.

The current understanding is that for an oil to be effective in preventing the formation of sulphuric acid that attacks the metal parts of an engine, it needs to have a high TBN (around 9 or 10). Since this number tends to fall rapidly as time goes on, this has an impact on the oil’s service life.

The issue is not so much how high the TBN is when the oil is new, which has an impact, but rather how stable this number is over time. A high TBN is no guarantee of oil quality, as it can mean the oil contains a medium or high level of sulphated ash to neutralise acids. This sulphated ash in the oil has a negative impact on the facility’s heat exchanger or catalytic converter, which can eventually clog up, resulting in expensive breakdowns.

Under 0.6% sulphated ash content key to reducing risk of breakdowns

The higher the sulphated ash content, the more deposition occurs in post-treatment systems. Fine ash is deposited in the catalytic converter and heat exchanger, resulting in increased exhaust pressure and decreased engine efficiency. If the pressure rises excessively, there is a risk of serious damage to the engine.

In addition, when the TBN is high, sulphated ash content also needs to be high – around 1% – to neutralise acids. However, sulphated ash makes the TBN unstable, causing it to fall. The higher the concentration of sulphated ash, the more rapidly the TBN will fall. This has a direct impact on the oil’s service life and drain intervals, as engine manufacturers recommend changing the oil when the TBN falls to 50% of its initial value.

The highly advanced technology used in the formulation of Texaco HDAX oils allows us to offer oils with under 0.6% ash content. The latest Texaco gas engine oils, Texaco HDAX 9200 and Texaco HDAX 9500, are low in sulphated ash. They have TBNs of 4.2 and 5.4 respectively, and are very stable over time – the true mark of the quality of Texaco HDAX premium gas engine lubricants.