Diesel for dummies

A report on the subtleties that differentiate one diesel engine from the other

With so many diesel-engined cars around, techno-geek acronyms seem to be the flavour of the day. Here we try to unravel the layers of acronyms and simplify some technical mumbo-jumbo. Acronyms like DI, IDI, CDI, TDI and CRDI, most of which are related to diesel engines make as much sense to the common man as National Award winning movies.

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Starting from the very basic diesel engine, the system works on the compression principle, i.e. the more you pressurise the hotter it gets. The idea is to increase the pressure inside the engine to such an extent that diesel automatically ignites. This is done through injecting diesel as a fine spray through an injector nozzle directly into the engine cylinder. This process is termed as Direct Injection (DI). However, as diesel enters the cylinder directly, it explodes instantly and hence DI engines are a bit noisy. The solution is Indirect Injection (IDI) where diesel enters a pre-combustion chamber before moving to the combustion chamber.

In India, the Mahindra Scorpio, Ford Mondeo and the Skoda Octavia use DI technology in various forms. All Tata engines use IDI tech and so do most Mahindra UV engines. Most importantly, the Toyota Qualis’ very capable engine is an IDI unit.

DI technology has recently metamorphosed into Common-Rail Direct Injection. This has bought diesel engines at par with the petrol one in terms of performance and resulted in a rise in diesel sales in Europe. As the name suggests, the technology uses a common rail where diesel is maintained at a very high pressure through an electric pump and individual injectors are connected to this rail. The technology was first perfected by Magneti Marelli but since then has been developed by Bosch and Delphi.

Globally, acronyms like CDI (Mercedes), CRDi (Hyundai), CRTDi (Hyundai), HDi (Peugeot), TDCI (Ford), JTD (Fiat and Alfa Romeo) and CTDI (Honda) are associated with the Common Rail technology.