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Engineering: The nature of problems
Engineering: The nature of problems

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4.2 From a need to a problem

So, working from the top down, the process starts with 'need' and 'problem'; see Figure 8.

Although we usually work by identifying a need that converts to a problem, that requires a solution, don't forget the extra arrow at the side, taking this first part of the process full circle. The questions that draw out the problem may also refine needs, or indeed extract further needs that were not stated, acknowledged or recognised at the very beginning. We've already looked at where these needs come from on a global scale but, unless you are an academic researcher or a totally independent inventor, by the time you reach this stage of design the need is usually coming very directly from a customer. The customer may be your employer, or an external client, who has somehow identified the need to develop a new product or significantly modify, improve or repair an existing one. It's obvious that the better the specification, the less time and money will be wasted in designing or producing a product or solution that doesn't meet the requirement.

Figure 8
Figure 8 Top part of Figure 7

There are different types of specification – for example, a 'product' specification and a 'functional' specification. If the supplier has more knowledge about the specific product than the customer then a functional specification is appropriate. However, if the supplier is just making a design to order then a full product description must be agreed. The writing of these formal documents that attempt to ensure that the solution matches the requirements has become something of an art. The specification may become a legal contract that binds the engineer to the task, instead of a practical guide to the route and therefore the solution to a problem. While nobody would argue that you should not have some sort of guarantee that you're going to get what you are paying for, it does seem to be a shame that the more control is exerted in this way, the less room there will be for creativity and hence innovation in devising solutions. Used properly, the specification can be arrived at by an open exchange of views and ideas between the two (or more) parties involved, so that the engineering team goes away to look for solutions with a clear record and understanding of both the need and the problem. An example of the process that leads to a specification can be seen in Box 5 From problem to specification.

Box 5 From problem to specification

Between the 1930s and 1980s, millions of industrial and domestic refrigerators and freezers were produced which used chlorofluorocarbon (CFC) gases as the refrigerant and in insulating materials. CFC gases didn't degrade the fridge, were non-flammable, not poisonous in the event of a leak, and seemed to be an ideal replacement for the original refrigerants such as ammonia that were smelly, corrosive, poisonous and not particularly efficient. However, it transpired that CFC gases are damaging to the environment, depleting the ozone layer that protects us from the harmful ultraviolet components of the sun's rays. A need was thus identified – for fridges and freezers that are environmentally friendly (Figure 9).

Figure 9
Figure 9 Piles of discarded fridges and freezers awaiting recycling

It is worth noting that this statement of needs is not at as fundamental a level as the earlier one in the water example. This illustrates the existence of the hierarchy of need. We need the ability to create cooled environments not only for keeping food fresh, but also for countless industrial processes. We are able to state the need in terms of fridges and freezers because there is a long history of market requirement and product development that moves the starting point of our need statement on from 'we need to keep our food fresh', through 'we need to make things cold' to 'we need fridges and freezers'.

There is a general principle here in the formulation of statements of need: the more fundamental the terms in which it is written, the greater the variety of solutions open for consideration, but the greater the possible number of dead ends. There is therefore a balance to be struck between maximising the chances of a really creative solution, and wasting time considering unsuitable ones. So, the statement 'the village needs a supply of clean water' leaves more options open than 'the village needs a water pump and filtration to get clean water from the river'.

To take this statement of the need the next step forward, we have to write a problem specification, which ideally will contain all the information necessary for working out a set of possible solutions.

Our need was stated as 'environmentally friendly fridges and freezers'. We can further refine this to 'we need alternative refrigerant gases to CFCs'. In doing this, we have excluded the possibility of using an alternative technology to the compression/expansion heat pump that is ubiquitous in refrigerators and freezers. There is a very good reason for this: the closed-cycle mechanical heat pump is the most energy-efficient known means of refrigeration, and to go to something that uses more energy could add an unacceptable environmental cost.

We can now state the requirements for the solution: A refrigerant gas with the following properties:

  • Not an ozone depleter

  • Compatible with conventional heat-pump technology

  • Non-corrosive

  • Non-hazardous (i.e. non-toxic, non-flammable)

  • Not an unacceptable source of some other pollution

  • Able to be manufactured in comparable volumes and costs to CFCs.

This is a technical specification. Clearly, it is at what could be called the top level; there are no numbers against any of these requirements. Once these have been added, though, we will have the beginnings of a formal document to bind the engineer to the task. The specification may even specifically exclude certain types of solution (as with the Hubble telescope repair).


There is a need to reduce the amount of pollution from airborne particulates in cities all over the world. A major factor is exhaust emissions from diesel engines. The search is on for an alternative fuel that doesn't produce the pollution locally.

Write a specification (as a list of bullet points) for an alternative automotive fuel that sets out the problem and is clear about the requirements that must be met in the solution.


The problem is to find or manufacture an alternative fuel for vehicles, because the existing fuels cause too much pollution in the towns and cities where they are used most intensively. The characteristics of the new fuel should include the following:

  • a significantly lower producer of particulate emissions

  • not a significantly worse producer of any other pollutants (including CO2, which would result if it is less energy efficient to produce and use)

  • no more toxic in unburnt form than existing fuels

  • no more hazardous than diesel

  • approximately the same cost to produce and use as existing fuels and possible to produce in similar volume (in terms not of litres, but of vehicle kilometres) to existing fuels

  • preferably compatible with existing internal combustion engines, i.e. no solutions that are 'innovation in context' (though not necessarily if a longer-term solution is wanted – vehicle lifetimes are relatively short, so a new technology could be brought in).